diff --git a/src/Speller.php b/src/Speller.php
index 71c4175..309a851 100644
--- a/src/Speller.php
+++ b/src/Speller.php
@@ -24,16 +24,21 @@ abstract class Speller
 	const CURRENCY_US_DOLLAR = 'USD';
 	
 	private static $languages = array(
-		'en' => languages\English::class,
-		'es' => languages\Spanish::class,
-		'et' => languages\Estonian::class,
-		'lt' => languages\Lithuanian::class,
-		'lv' => languages\Latvian::class,
-		'ru' => languages\Russian::class,
+		self::LANGUAGE_ENGLISH    => languages\English::class,
+		self::LANGUAGE_ESTONIAN   => languages\Estonian::class,
+		self::LANGUAGE_LATVIAN    => languages\Latvian::class,
+		self::LANGUAGE_LITHUANIAN => languages\Lithuanian::class,
+		self::LANGUAGE_RUSSIAN    => languages\Russian::class,
+		self::LANGUAGE_SPANISH    => languages\Spanish::class,
 	);
 	
 	private static $currencies = array(
-		'EUR', 'LTL', 'LVL', 'RUR', 'USD', 'GBP',
+		self::CURRENCY_EURO,
+		self::CURRENCY_BRITISH_POUND,
+		self::CURRENCY_LATVIAN_LAT,
+		self::CURRENCY_LITHUANIAN_LIT,
+		self::CURRENCY_RUSSIAN_ROUBLE,
+		self::CURRENCY_US_DOLLAR,
 	);
 	
 	protected $minus;
diff --git a/src/languages/English.php b/src/languages/English.php
index f28932e..70c6177 100644
--- a/src/languages/English.php
+++ b/src/languages/English.php
@@ -99,30 +99,30 @@ protected function spellExponent($type, $number, $currency)
 	protected function getCurrencyName($type, $number, $currency)
 	{
 		static $names = array(
-			'EUR' => array(
+			self::CURRENCY_EURO => array(
 				'whole'   => array('euro', 'euro'),
 				'decimal' => array('cent', 'cents'),
 			),
-			'LTL' => array(
-				'whole'   => array('litas', 'litai'),
-				'decimal' => array('centas', 'centai'),
+			self::CURRENCY_BRITISH_POUND => array(
+				'whole'   => array('pound', 'pounds'),
+				'decimal' => array('penny', 'pennies'),
 			),
-			'LVL' => array(
+			self::CURRENCY_LATVIAN_LAT => array(
 				'whole'   => array('lat', 'lats'),
 				'decimal' => array('santim', 'santims'),
 			),
-			'RUR' => array(
+			self::CURRENCY_LITHUANIAN_LIT => array(
+				'whole'   => array('litas', 'litai'),
+				'decimal' => array('centas', 'centai'),
+			),
+			self::CURRENCY_RUSSIAN_ROUBLE => array(
 				'whole'   => array('ruble', 'rubles'),
 				'decimal' => array('kopek', 'kopeks'),
 			),
-			'USD' => array(
+			self::CURRENCY_US_DOLLAR => array(
 				'whole'   => array('dollar', 'dollars'),
 				'decimal' => array('cent', 'cents'),
 			),
-			'GBP' => array(
-				'whole'   => array('pound', 'pounds'),
-				'decimal' => array('penny', 'pennies'),
-			),
 		);
 		
 		if (!isset($names[$currency]))
diff --git a/src/languages/Estonian.php b/src/languages/Estonian.php
index 7e4b6d1..87e2e85 100644
--- a/src/languages/Estonian.php
+++ b/src/languages/Estonian.php
@@ -116,30 +116,30 @@ protected function spellExponent($type, $number, $currency)
 	protected function getCurrencyName($type, $number, $currency)
 	{
 		static $names = array(
-			'EUR' => array(
+			self::CURRENCY_EURO => array(
 				'whole'   => array('euro', 'eurot'),
 				'decimal' => array('sent', 'senti'),
 			),
-			'LTL' => array(
-				'whole'   => array('litt', 'litti'),
-				'decimal' => array('sent', 'senti'),
+			self::CURRENCY_BRITISH_POUND => array(
+				'whole'   => array('nael', 'naela'),
+				'decimal' => array('penn', 'penni'),
 			),
-			'LVL' => array(
+			self::CURRENCY_LATVIAN_LAT => array(
 				'whole'   => array('latt', 'latti'),
 				'decimal' => array('santiim', 'santiimi'),
 			),
-			'RUR' => array(
+			self::CURRENCY_LITHUANIAN_LIT => array(
+				'whole'   => array('litt', 'litti'),
+				'decimal' => array('sent', 'senti'),
+			),
+			self::CURRENCY_RUSSIAN_ROUBLE => array(
 				'whole'   => array('rubla', 'rubla'),
 				'decimal' => array('kopikas', 'kopikat'),
 			),
-			'USD' => array(
+			self::CURRENCY_US_DOLLAR => array(
 				'whole'   => array('dollar', 'dollarit'),
 				'decimal' => array('sent', 'senti'),
 			),
-			'GBP' => array(
-				'whole'   => array('nael', 'naela'),
-				'decimal' => array('penn', 'penni'),
-			),
 		);
 		
 		if (!isset($names[$currency]))
diff --git a/src/languages/Latvian.php b/src/languages/Latvian.php
index 0a7b89d..e29fd44 100644
--- a/src/languages/Latvian.php
+++ b/src/languages/Latvian.php
@@ -106,7 +106,7 @@ private function spellSingle($digit, $isDecimalPart, $currency)
 			9 => 'deviņas',
 		);
 		
-		if ($isDecimalPart && ($currency === 'RUR'))
+		if ($isDecimalPart && ($currency === self::CURRENCY_RUSSIAN_ROUBLE))
 		{
 			// russian kopek nouns are feminine gender in Latvian
 			return $singlesFeminine[intval($digit)];
@@ -146,30 +146,30 @@ protected function spellExponent($type, $number, $currency)
 	protected function getCurrencyName($type, $number, $currency)
 	{
 		static $names = array(
-			'EUR' => array(
+			self::CURRENCY_EURO => array(
 				'whole'   => array('eiro', 'eiro', 'eiro'),
 				'decimal' => array('cents', 'centi', 'centu'),
 			),
-			'LTL' => array(
-				'whole'   => array('lits', 'liti', 'litu'),
-				'decimal' => array('cents', 'centi', 'centu'),
+			self::CURRENCY_BRITISH_POUND => array(
+				'whole'   => array('mārciņa', 'mārciņas', 'mārciņu'),
+				'decimal' => array('penijs', 'peniji', 'peniju'),
 			),
-			'LVL' => array(
+			self::CURRENCY_LATVIAN_LAT => array(
 				'whole'   => array('lats', 'lati', 'latu'),
 				'decimal' => array('santīms', 'santīmi', 'santīmu'),
 			),
-			'RUR' => array(
+			self::CURRENCY_LITHUANIAN_LIT => array(
+				'whole'   => array('lits', 'liti', 'litu'),
+				'decimal' => array('cents', 'centi', 'centu'),
+			),
+			self::CURRENCY_RUSSIAN_ROUBLE => array(
 				'whole'   => array('rublis', 'rubļi', 'rubļu'),
 				'decimal' => array('kapeika', 'kapeikas', 'kapeiku'),
 			),
-			'USD' => array(
+			self::CURRENCY_US_DOLLAR => array(
 				'whole'   => array('dolārs', 'dolāri', 'dolāru'),
 				'decimal' => array('cents', 'centi', 'centu'),
 			),
-			'GBP' => array(
-				'whole'   => array('mārciņa', 'mārciņas', 'mārciņu'),
-				'decimal' => array('penijs', 'peniji', 'peniju'),
-			),
 		);
 		
 		if (!isset($names[$currency]))
diff --git a/src/languages/Lithuanian.php b/src/languages/Lithuanian.php
index fdf5b86..9022d9b 100644
--- a/src/languages/Lithuanian.php
+++ b/src/languages/Lithuanian.php
@@ -124,30 +124,30 @@ protected function spellExponent($type, $number, $currency)
 	protected function getCurrencyName($type, $number, $currency)
 	{
 		static $names = array(
-			'EUR' => array(
+			self::CURRENCY_EURO => array(
 				'whole'   => array('euras', 'eurai', 'eurų'),
 				'decimal' => array('centas', 'centai', 'centų'),
 			),
-			'LTL' => array(
-				'whole'   => array('litas', 'litai', 'litų'),
-				'decimal' => array('centas', 'centai', 'centų'),
+			self::CURRENCY_BRITISH_POUND => array(
+				'whole'   => array('svaras', 'svarai', 'svarų'),
+				'decimal' => array('pensas', 'pensai', 'pensų'),
 			),
-			'LVL' => array(
+			self::CURRENCY_LATVIAN_LAT => array(
 				'whole'   => array('latas', 'latai', 'latų'),
 				'decimal' => array('santimas', 'santimai', 'santimų'),
 			),
-			'RUR' => array(
+			self::CURRENCY_LITHUANIAN_LIT => array(
+				'whole'   => array('litas', 'litai', 'litų'),
+				'decimal' => array('centas', 'centai', 'centų'),
+			),
+			self::CURRENCY_RUSSIAN_ROUBLE => array(
 				'whole'   => array('rublis', 'rubliai', 'rublių'),
 				'decimal' => array('kapeika', 'kapeikos', 'kapeikų'),
 			),
-			'USD' => array(
+			self::CURRENCY_US_DOLLAR => array(
 				'whole'   => array('dolaras', 'dolarai', 'dolarų'),
 				'decimal' => array('centas', 'centai', 'centų'),
 			),
-			'GBP' => array(
-				'whole'   => array('svaras', 'svarai', 'svarų'),
-				'decimal' => array('pensas', 'pensai', 'pensų'),
-			),
 		);
 		
 		if (!isset($names[$currency]))
diff --git a/src/languages/Russian.php b/src/languages/Russian.php
index fc359bf..0241e1d 100644
--- a/src/languages/Russian.php
+++ b/src/languages/Russian.php
@@ -107,7 +107,7 @@ private function spellSingle($digit, $groupOfThrees, $isDecimalPart, $currency)
 		);
 		
 		if (($groupOfThrees === 2) // thousands
-			|| ($isDecimalPart && ($currency === 'RUR'))) // russian kopeks
+			|| ($isDecimalPart && ($currency === self::CURRENCY_RUSSIAN_ROUBLE))) // russian kopeks
 		{
 			return $singlesFeminine[intval($digit)];
 		}
@@ -158,30 +158,30 @@ protected function spellExponent($type, $number, $currency)
 	protected function getCurrencyName($type, $number, $currency)
 	{
 		static $names = array(
-			'EUR' => array(
+			self::CURRENCY_EURO => array(
 				'whole'   => array('евро', 'евро', 'евро'),
 				'decimal' => array('цент', 'цента', 'центов'),
 			),
-			'LTL' => array(
-				'whole'   => array('лит', 'лита', 'литов'),
-				'decimal' => array('цент', 'цента', 'центов'),
+			self::CURRENCY_BRITISH_POUND => array(
+				'whole'   => array('фунт', 'фунта', 'фунтов'),
+				'decimal' => array('пенни', 'пенса', 'пенсов'),
 			),
-			'LVL' => array(
+			self::CURRENCY_LATVIAN_LAT => array(
 				'whole'   => array('лат', 'лата', 'латов'),
 				'decimal' => array('сантим', 'сантима', 'сантимов'),
 			),
-			'RUR' => array(
+			self::CURRENCY_LITHUANIAN_LIT => array(
+				'whole'   => array('лит', 'лита', 'литов'),
+				'decimal' => array('цент', 'цента', 'центов'),
+			),
+			self::CURRENCY_RUSSIAN_ROUBLE => array(
 				'whole'   => array('рубль', 'рубля', 'рублей'),
 				'decimal' => array('копейка', 'копейки', 'копеек'),
 			),
-			'USD' => array(
+			self::CURRENCY_US_DOLLAR => array(
 				'whole'   => array('доллар', 'доллара', 'долларов'),
 				'decimal' => array('цент', 'цента', 'центов'),
 			),
-			'GBP' => array(
-				'whole'   => array('фунт', 'фунта', 'фунтов'),
-				'decimal' => array('пенни', 'пенса', 'пенсов'),
-			),
 		);
 		
 		if (!isset($names[$currency]))
diff --git a/src/languages/Spanish.php b/src/languages/Spanish.php
index aeaa3ce..ff6f668 100644
--- a/src/languages/Spanish.php
+++ b/src/languages/Spanish.php
@@ -131,30 +131,30 @@ protected function getCurrencyName($type, $number, $currency)
 	{
 		// TODO some of these spellings are extremely hard to find and are probably incorrect
 		static $names = array(
-			'EUR' => array(
+			self::CURRENCY_EURO => array(
 				'whole'   => array('euro', 'euros'),
 				'decimal' => array('centime', 'centimes'),
 			),
-			'LTL' => array(
-				'whole'   => array('litas', 'litas'),
-				'decimal' => array('cent', 'cents'),
+			self::CURRENCY_BRITISH_POUND => array(
+				'whole'   => array('libra esterlina', 'libras esterlinas'),
+				'decimal' => array('penique', 'peniques'),
 			),
-			'LVL' => array(
+			self::CURRENCY_LATVIAN_LAT => array(
 				'whole'   => array('lat', 'lats'),
 				'decimal' => array('sentim', 'sentims'),
 			),
-			'RUR' => array(
+			self::CURRENCY_LITHUANIAN_LIT => array(
+				'whole'   => array('litas', 'litas'),
+				'decimal' => array('cent', 'cents'),
+			),
+			self::CURRENCY_RUSSIAN_ROUBLE => array(
 				'whole'   => array('rublo ruso', 'rublos rusos'),
 				'decimal' => array('kopek', 'kopeks'),
 			),
-			'USD' => array(
+			self::CURRENCY_US_DOLLAR => array(
 				'whole'   => array('dólar estadounidense', 'dólares estadounidenses'),
 				'decimal' => array('centavo', 'centavos'),
 			),
-			'GBP' => array(
-				'whole'   => array('libra esterlina', 'libras esterlinas'),
-				'decimal' => array('penique', 'peniques'),
-			),
 		);
 		
 		if (!isset($names[$currency]))