Adding less common languages

[mitra42]

Its nice that the module includes several major languages, but our project is looking at nodes in developing countries with a pilot project in Indonesia which will want Indonesian and English as the two choices.

I can think of multiple ways of doing this - and am interested if @Juerd you have a preference.

1: Fork the repo - add the language and developers can include this version of the library instead of yours,
2: Export _WSL_T in the library so that an application can overwrite the strings based on the language chosen - but then every developer has to do it for themselves for any language they want.
3: Submit a PR that adds Indonesian to the main library. In this case, I'd suggest that Indoneesian is not added to LANGUAGE_ALL which makes it cost-free to add any number of less common languages (e..g the app has to #define LANGUAGE_ID to get that as one of the options).

I'm happy to do any of these but keen to get your preference first.