Date and number may have different “translations” (or say msgstr) in different locales. The example I gave is used in applications and the context would mark that translators can change the format according their usage of date format.
Honestly (the source code of) Indico is quite unfriendly at this point; not only in the html/js but also somewhere in the main programs. IIRC I have sent a pull request to Indico mentioning all those d-m-y or m-d-y format usage…