I tested the Yandex engine extensively. It's not perfect (no machine translation ever is), but it's much better at translating between Slavic languages (say, Polish to/from Russian or Slovak) than Google Translate (here's my evaluation). As it's but an experimental feature within experimental feature, we didn't find it necessary to vote it, but we had a discussion at our Village Pump (link) and nobody opposed.
|Open||None||T76456 Language Engineering tracker of trackers (tracking)|
|Open||None||T76454 [Epic] ContentTranslation - MT support|
|Open||None||T86700 Add more machine translation services (tracking)|
|Resolved||KartikMistry||T121053 Enable Yandex for Polish Wikipedia|