Internationalisation & at least 1 localisation

[Montandalar]

Digtron has the stub of support for internationalisation, with a number of strings written into a template file by Facedeer. But it appears that these files haven't been touched in years and predate Minetest 5's translation features, instead using intllib. Most of the source files seem to have wrapped the strings that are supposed to be translated at least.

• Check all source files for unwrapped player-facing strings and wrap them with S where appropriate
• Change all references to intllib to instead use Minetest 5 localisation
• Write a complete English template file, possibly based on the original work by Facedeer.
• Complete a reference localisation in a common language like German.

[ksandronline]

Maybe me.