@Merxa
I use the same file in all folders (languages), I use the English version of the plugin, and i dont change oxide.lang to "ru", i think, that its "en", becouse all server messages on English.
And most importantly, try rebooting the server after making all the changes, because I've encountered a problem where after making changes to the files I didn't see any changes in the game and it was confusing, but after rebooting everything fell into place. If you want to support multiple languages (ru for Russian and en for English), I don't know what difficulties you might have, because I use one Russian file in all folders so people can play on the English version of the game and see everything in Russian, since I don't have an EU server, but somehow I think the problem is only with rebooting the server, because the plugin or oxide seems to use some kind of cache, which sometimes prevents some data from being updated without rebooting the server.
Config:
"Marker Name": "База для Рейда",
Lang:
"ModeEasy": "<color=#00C100>Легкая</color>",
"ModeMedium": "<color=#C1C100>Средняя</color>",
"ModeHard": "<color=#C10000>Сложная</color>",
"ModeExpert": "<color=#0000C1>Экспертная</color>",
"ModeNightmare": "<color=#505050>Кошмарная</color>",