Hi Mahmoud,
From my understanding, Messenger currently determines its UI language from the customer's browser language preferences. If the detected language matches one of the configured supported languages, Messenger uses that language; otherwise, it falls back to the configured default language. I haven't found a documented deployment parameter, SDK command, or custom attribute that allows the language to be changed dynamically after Messenger has loaded.
I also came across the following Ideas Lab request, which appears to match your use case exactly:
https://genesyscloud.ideas.aha.io/ideas/DXWMM-I-135
The Product Management team has marked it as Planned, with the comment:
"We continue to plan for this feature on our upcoming Messenger roadmap, we'll be providing updates as soon as we move into Design phase."
Hopefully this will address scenarios like single-page applications where the website language changes without requiring a full page reload.
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Phaneendra
Technical Solutions Consultant
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