AMO search should include entries in results that differ only in accented or umlauted characters, e.g. entering "jokulsarlon" should include "Jökulsárlón" in its results. That is needed to not require people to be able to enter special characters in all kinds of languages but still be able to find add-ons with such characters in their names.
We solved this on Marketplace in bug 907843. It would be useful to review what happened there to fix this.
Thanks for filing this. In an effort to not drown in existing reports we're aggressively closing old enhancements and bugs to get the buglist to a reasonable level so we can scope and process bug sprints in an effective manner. Patches for this bug are still welcome.