Please check those threads and let me know if the behavior you’re seeing matches what’s described there. If so, the solution discussed in those posts may apply to this case as well.
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I’ve completed additional tests and checks, and it appears that the issue is still the same as before. Output compression is very likely still enabled on your server, and it is affecting the Advanced Translation Editor.
I also verified the database table collations, and they are all correct.
As an additional test, I temporarily switched WPML to use the Classic Translation Editor (WPML → Settings) and checked the translation again. The behavior remains the same: the server is returning binary/compressed data instead of plain text. I’ve attached screenshots for your reference.
Unfortunately, this cannot be fixed on the WPML side. A change to your server configuration is required, followed by a server restart.