Hello! I am a Translation Manager for International Translation Services. Yes, this issue has been happening for a couple of days, it is a Roblox issue but there is a fix that might work for some. If you have a direct link to the game you want to translate, you can still access the portal and translate without any issues. My team has contacted the Roblox Staff to let them know about this issue.
I hope this helps clear out any questions you might have had.
I got the same issue. I contacted roblox in Emails and I haven’t gotten so far. I tried to clear my cookies and files of roblox but it didn’t help (they suggested it). I still am in contact with them and I (and ofc the lovely team of ITS, who I just noticed in the comments) are trying to get it sorted out :>.
Have you tried using the direct link for the game you want to translate? If you translated the game before you can usually find it in your browser history . That is the only known solution as the moment, as Roblox is completely changing the develop tab.