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This limitation is caused by Atlassian, and relates to this ticket with Atlassianthe fact that JQL doesn't support translations, there's been several tickets on this like this one for instance. As soon as Atlassian resolves the ticket, we will be able to display field names in the search field as well. The good news is that we managed to make it so that epic is not displayed.
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Like with other apps, when you upgrade your Jira, ensure that you have the compatible version of the app installed, no additional action or configuration is necessary.
What if I use third party systems like Jira Align, how will the translations work?
Translations are made in Jira native screens only, and third party applications are not covered.
If you have a system that uses REST services to communicate with Jira, then you have some service Jira account that makes changes to Jira entities (using which REST API calls are made). Such service account must have a non-translated locale configured in the user profile, because Jira doesn't support working with translated entities in the services.
For example, the default translations are applied to EN_US locale. This means that the service account must have a non EN_US locale, EN_UK for instance.