I am missing the function, that would allow me to switch spell-check languag or even better, if the spell-check would detect the language from a word...
As many, I am mixing German and English in my emails.

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Every writing Desktop Software (take LibreOffice) has the possibility to choose if the spell checker is activated or not and in which language the check takes place without depending on the language OS that is configured.

Many people know and write in multiple languages. Proofing language should not be tied to application language. I want to configure multiple language I commonly write in and spellchecker automatically picks the one I write in, or allow me to quickly switch between my languages from a drop down. Desktop app is most important to me, but mobile apps should also have this.

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I use English interfaces on the web and on my desktop, yet I write and read in multiple languages. Not being able to spellcheck in the email app is a drag and slows down my productivity.

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how is it that you're launching new services but the mail client app doesn't support multiple languages ??

please focus on the basics before launching anything else

Still an issue on current desktop versions (Windows 11). No OS-level or in-app workaround exists.

I have to write emails in Spanish and English and the lack of this functionality is a real pain.

At least Isaac's workaround worked.

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As a workaround -

1) Make sure Proton Mail are closed.
2) Open the following file.config/Proton Mail/Partitions/app/Preferences (very important it is this exact one!)
3) Change the dictionaries property to the language/locale which you want to have spelling for. E.g. here I have selected US English and Spanis; in Spain. :{"partition":{"per_host_zoom_levels":{"4966268783509498187":{}}},"spellcheck":{"dictionaries":["es-ES","en-US"],"dictionary":""}}
4) Save the file.
5) Open Proton Mail again.

This is a really big deal breaker and I hope they implement this soon.

I asked for the same feature when the beta version of Proton Mail desktop app was released and it's still not implemented.
That's the only reason why i can't use it and the first time I'm disappointed by the lack of advancement from Proton Team.
This is basic to implement and critical for most users in the world since we need to write in at least 2 languages nowadays.

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I completely agree — having the ability to manually configure the spell-checker language in the Proton Mail desktop app would be extremely useful. Many users write emails in multiple languages, and relying only on the OS language creates unnecessary limitations. A built-in language selector (similar to what browsers use) would make the app much more flexible and user-friendly.

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