Page "Help:Interlanguage links" Paragraph 83

For projects like Meta, a missing leading colon has no effect, because Meta doesn't support interlanguage links.

For Wikipedia and similar projects, it is a major difference.

The mutual order of interlanguage links is preserved, but otherwise the positions within the wikitext are immaterial, again the same rule as for categories.

Usually they are put at the end.

With section editing, they appear in the preview, if they are in the section being edited.

A link to the project itself ( hence, also a link to the page itself ), even if referred to with the project prefix, appears in-page.