Update translations

[svartkanin]

This is an update to the translations and fixes #1237

Changes

• By displaying the respective language in it's own language we'll now always load the cyrillic font to display the Cyrillic languages in the selection menu correctly; this is still done in a try-block so things should not blow up if the font can't be found
• Added pt_BR to the list, which already had a translation file but wasn't picked up before
• Added a percentage next to the language which indicates the amount of translations available for the language, this is to give a user some hints on how well the language is currently supported (and might encourage users to contribute to it :) )
• Modified the main README to include a section about the supported languages and a link to the guide how to contribute to the translations @Torxed let me know if there's any concerns with this :)