A minimal repro for the issue of helpers breaking when called in the unambiguous way:
{{(translate)}}
It turns out that no matter what kind of helper you have (class-based, functional or plain-function), they all break when called as above.
What matters is that staticHelpers be set to false in the config.
If it is, it breaks with the following:
Uncaught TypeError: func is not a function
at Compilers.compile (opcode-compiler.js:417:1)
at expr (opcode-compiler.js:587:1)
at opcode-compiler.js:1799:1
at SwitchCases (opcode-compiler.js:943:1)
at opcode-compiler.js:1798:1
at Compilers.compile (opcode-compiler.js:417:1)
at compileStatements (opcode-compiler.js:2070:1)
at maybeCompile (opcode-compiler.js:2049:1)
at CompilableTemplateImpl.compile (opcode-compiler.js:2032:1)
at Object.evaluate (runtime.js:2973:1)
If the staticHelpers is set to true, it works fine.