Sidebar headers are not translated in preview

[MariaNHN]

To recreate:

1. Create new form
2. Add sidebar items (SOT-1, SOT-2 and SOT-3) with some text
3. Create a new language in the form, and translate the sidebar text
4. Preview the form, and see that the sidebar headers are still in Norwegian

[mgunnerud]

@MariaNHN texts in preview are not translated yet, I suggest this issue can be fixed as a part of a larger task for preview translations

[MariaNHN]

Ok