Currently, it is not possible to have a Map\URI matcher containing a string with umlauts.

Steps to reproduce:

1. Prepare a test installation of eZ Publish 5.4, updated to 5.4.6;
2. Change the URLTransformation in legacy site.ini:

settings/override/site.ini.append.php

[URLTranslator]
TransformationGroup=urlalias_iri

3. Clear legacy cache;
4. Modify ezpublish.yml to have the "ezdemo_site" siteaccess matching the URIText "flüchtlinge":

ezpublish:
    siteaccess:
        match:
            Compound\LogicalAnd:
                my_compound_rule_1:
                    matchers:
                        Map\URI:
                            'flüchtlinge': true
                        Map\Host:
                            example.com: true
                    match: ezdemo_site

5. Clear symfony cache;
6. Try to access this link:
http://example.com/flüchtlinge/eZ-Mountains -> FAILS, with a "Module not found The requested module flüchtlinge could not be found." message.

NOTE: the following steps exist to verify that the problem was being caused by the umlaut

7. Edit ezpublish.yml and remove the umlaut from "flüchtlinge" in the "Map\URI" matcher:

ezpublish:
    siteaccess:
        match:
            Compound\LogicalAnd:
            my_compound_rule_1:
                matchers:
                    Map\URI:
                        'fluchtlinge': true
                    Map\Host:
                        example.com: true
                match: ezdemo_site

8. Clear symfony cache;
9. Try to access this link:
http://example.com/fluchtlinge/eZ-Mountains -> WORKS