I have created a custom section. For this section I also have created a lang/en-us.xml file:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<language alias="en" intName="English (US)" localName="English (US)" lcid="" culture="en-US">
  <area alias="sections">
   <key alias="formDataSection">Formulierdata</key>
  </area>
</language>

When I run the project locally the section is translated the way it should. I see the section with the correct translation: 'Formulierdata', but when I deploy it to Azure, I see the notorious brackets: '[formDataSection]'.

I can confirm that lang/en-us.xml is deployed on Azure. I can see this when I open Kudu and browse the files of the site.

I can also confirm that the language of the logged in user is set to 'en (US)' in the profile.

There are no multiple languages activated in Umbraco, only en-us.

This problem occurs in every Azure environment (test, acceptance, production).

What do I need to do to fix this?

Thanks.