Add a return type to helpers.check_prototype_translations()

[KiwiHawk]

Can you please change `helpers.check_prototype_translations()` to return a boolean? Or an integer with the number of errors. I'm calling it as part of Angel's unit tests. I currently have no way of making the test fail if untranslated strings are detected!

With the update to 2.0, we have a lot of recipes missing locale as recipes no longer inherit the name of their `main_product` unless the recipe and item/fluid have the same name.

[Bilka]

As far as I'm aware this is not possible because the result is not deterministic because it depends on the current locale.

[KiwiHawk]

What about if the function accepted a language?

[Bilka]

The game doesn't load anything besides the current locale.

[curiosity]

What about if the function accepted a language?

Though IDK if this was changed in 2.0, but identity is not guaranteed for locale, unlike the rest of the mod files. It's ignored when computing mod checksum and such.