Steps to replicate the issue (include links if applicable):

Given:
[[Translatable]]:

<translate>
== Header == <!--T:1-->
</translate>

[[Transcluder]]:

<translate><!--T:1-->
Hello
</translate>
{{lsth:Translatable|Header}}

• Create [[Translatable]] page as above, mark it for translation and translate it.
• Create a [[Transcluder]] page as above, mark it for translation and translate it.

What happens?:

• In source language, [[Transcluder]] well displays [[Translatable]] section.
• In translation pages (e.g. [[Transcluder/fr]]), lsth does not display anything.

What should have happened instead?:
In translation pages, the section should be actually transcluded.

Other information:
Follow-up of T47096 which allowed to transclude translatable pages without any hack.

The workaround is to manually add section labels, to use {{lst:}} instead.