Please add there also the "Add more languages here" comment:
<Localization Enabled="true">
<SupportedLanguages DefaultLanguage="en" MergeBehavior="Append">
<SupportedLanguage>en</SupportedLanguage>
<!-- Add more languages here -->
</SupportedLanguages>
In TrustFrameworkLocalization.xml we have the list of supported languages:
Please add there also the "Add more languages here" comment: