Jira system language overrides default support language and browser language

Issue Summary

In anonymous portal, if the Jira system language is set to, for example, Danish, German, Portuguese, Spanish, the customers will see the portal in system language (the login page/portal text is in system language) despite having the project's default support language set to English and the customer's browser language set to any other language.

Steps to Reproduce

1. Go to the project and set English as the default language support and add Danish/Portuguese/German/Spanish as a language visible to customer.
2. Go to Jira settings and set system language to Danish/Portuguese/German/Spanish.
3. Go to the browser settings and change browser language setting to French or any other language other than English.
4. Make sure to clear browser cache and cookies,
5. Open Incognito browsing mode and go to the portal.

Expected Results

The customer portal login page should be showing as English(UK) since the default support language of the project is set to English(UK), while the other portal elements/text should be following the browser languages of the user.

For example - if the user's browser language is set to French:

• Request types should be in English(UK)
• Portal elements such as login page, uneditable text elements should be in French.

Actual Results

The login page is showing as Danish/Portuguese/German/Spanish even though the default support language of the project is set to English(UK). So the Jira system language is overriding the default support language and browser language.

For example - if the user's browser language is set to French:

• Request types is showing as Danish
• Portal elements such as login page, uneditable text elements is also showing in Danish.

Workaround

• Change the Jira system language to English(UK) and set Jira user profile to Danish/Portuguese/German/Spanish instead if the users want Jira to be in Danish/Portuguese/German/Spanish.