I completed a UK translation for the the game, following the Translation Thread, using poedit.
The translation created two files - a strings.po and a strings.mo. I added the strings.po to the correct game folder and the translation has appeared in game. However there seems to be a font size and style change occurring.
I've attached screenshots of the original game and of the game with the strings.po file added to the OxygenNotIncluded\OxygenNotIncluded_Data\StreamingAssets\Mods folder.
Game Screen - Original
Game Screen - Translation
Menu Screen - Original
Menu Screen - Translation
Added strings.po translation file to the mods folder