With some fantastic technical AND language insights, @blinkinaday has cracked the key to the first comment. Here's what they did in their own words:
Just decoded it. Since it was a reply comment to a user that managed to discover the fez alphabet, I assumed it was along the way of: "congratulations". so I tried to decode it from known plaintexts like "very well", "very good", or "well done" (I assumed the space patterns matched the plaintext).
Assuming "well done" were the first two words, and shifting the supposed key-text by the cipher text, @blinkinaday discovered the key, and the full message.
well done ..................
bikq hnsi ryex yymjh
fezf ezfe ...
Therefore the key to try must be "FEZ". If we try that key against the full message:
"bikq hnsi ryex yymjh"
"well done stay tuned"
Nice work @blinkinaday!
Sadly the key doesn't seem to work on the second comment, so let's keep trying!
Update 2: Sorry everyone I originally posted the wrong key (off by one error!). Thanks again to @blinkinaday for the update. You can try the decoding using this website (instead of what I previously posted):