As you may be aware, the PMUser site’s language (logged in browser and SPE) is governed by the selected system’s display language.While the language may be changed and cached during logged in browser session, that change is not stored/cached for the SPE for security reasons.
This is by design. An enhancement request (TF00690972) has been created detailing the feature: ability to enforce a default language for the PMUser’s site, despite of/to override the selected system’s display language.
The product team will evaluate the request and this feature may become available on a future release of the product.
Please refer to this article for updates or contact support referencing the Enhancement Request ID: TF00690972.