Weird type declarations for stemmers?

[sweetpalma]

I have recently updated the library version from v6 to v8, and now my custom stemmer is reporting type errors:

It seems like those new interface methods were added fairly recently, and only a few selected languages (like English and French) are actually using them. Is there any description or example of how these methods should work for other languages?

Also, additional question to these methods - do you actually need them in the global library declaration?