I've had the same difficulty at times. Even on FT, unless it's an airline with a heavy and active forum or captured in a trip on the Trip Report forum, recent and relevant reviews can be sparse at times.

The dedicated airline forum part of Trip Advisor is mostly useless rants by a lot of one-hit wonders. I've had some occasional luck searching through trip reports and posts in the regular TA forum for a destination that the airline flies to a lot (especially the place I'm going to). Sometimes people will mention their experience as part of their trip report and it can be (but isn't always!) less ranty...or someone will inquire about a given airline and then some folks will mention their experiences, the airline reputation, etc.. It's not the best but can produce some decent info (and again is a bit better than the "airlines" forum part of TA).

Along the same lines, I'll look through trip reports on travel blogs and other travel sites (sometimes Youtube can be a good source for inflight reviews) to see what airline experience they had and any general airline advice for the destination. This tends to produce some good inputs, often with plenty of photos.

Sometimes googling will produce articles or posts from other countries which, with the help of google translate, can be worthwhile.