@Vlad_Piratov Can you see any errors? or the file is just completely ignored? Could you make sure that ru-RU.json doesn't contain any metadata for translators? it should look like "key": "value", not "key: { "text":..., "comment": ... }
"translations": ["x-pack/plugins/translation/translations/ru-RU.json"]
should be "translations": ["x-pack/plugins/translations/translations/ru-RU.json"]