Hikage1983: Alright so yesterday for whatever reason the store was stuck on USD when logged via Galaxy.
It was also briefly the case for the website but clearing cookies/logins may have helped in fixing it.
So today after seeing that the issue had persisted on Galaxy, i went into C: > ProgramData (this is a hidden folder mind you) > GOG.com > Galaxy > webcache and wiped the contents ( tho i suspect that was overkill since cookies seem to be stored in webcache>common.)
At any rate, this restored the in-Galaxy store to EUR for me, so i am sharing this info in case someone needs it.
I suspect it would work in case the store display language is wrong too.
Note: Do NOT delete anything outside the webcache folder.
Note2: Do not forget to shut down Galaxy before attempting the above as restarting the client will recreate the files in webcache.
Thank you - this worked a treat! Been pulling my hair out up until now. :)