Add CS (Czech) and SK (Slovak) languages

[Vojtas87]

Text instructions localized into Czech and Slovak languages.

[1ec5]

Thanks for this localization! Just double-checking, did you add these translations to Transifex first and then synchronize this repository with Transifex, or did you translate these files manually? If you translated them manually, please see these instructions for ensuring that the translations stay in sync. It may be possible to import the translations into Transifex if necessary.

[yuryleb]

BTW @Vojtas87, maybe both Czech and Slovak translations need for grammar transformations like Russian has? I could help with this 😉

[Vojtas87]

Ouch, I'm sorry gentlemen. I just pushed my manual translations without reading the instructions. I looked into Transifex, but "unfortunately" there are Czech (82,2%) and Slovak (68,5%) languages, so I can't add my version. Also I'm not able to check these existing partial translations to finish them (if I searched well). So I'm sorry again, just decline this pull request, please. Have a nice day.

[yuryleb]

No problem actually, just register in Transifex as translator and try to fix/update translations right there after. I suppose those existing translations were created even with Google Translate.
Please don't forget about my question for grammar transformations 😉

[1ec5]

The ones in Transifex were donated by the European Commission (#223), but by the time we received them, they had already become outdated, omitting many of the strings that had been added to facilitate turn-by-turn navigation. I’m not very familiar with the EC’s translation program, but if you see any errors, don’t hesitate to correct them.