Make Osm:Browse.common_details.coordinates_html, Osm:Browse.note.coordinates_html and Osm:Diary_entries.location.coordinates optional
THe description may be just an indication. In my opinion it is superfluous indication, as all translatable messages use "en" for their default, as long as they are not translated. Note translating them is still a bad idea: it's still best to confirm that the English term is actually the one used for "coordinates", which is obviously not correct in all non-Latin languages and most Latin-written languages that have their own word (even if it's an orthographic variant). E.g. in French, "coordinates" would look wrong, we want "coordonnées"...
Optional messages are for things whose translation is not needed for common users, e.g.
- messages in technical logs, mostly intended for being reported to a bug maintainer, and not directly part of the UI (even if you can see them by pressing a "Detailed" button, or if they occur on the middle of log files containing many untranslated items such as fragment of code, track traces, encoded values in hexadecimal or compressed bitfields, locale-neutral timestamps, CPU/resource usage, objects/classes names, API names...
- or if they are about messages only seen by a few authorized admins of the service; or just a few users choosing to use an "advanced mode" or participating in "beta tests".
- or if they are about transitory messages that won't last for long, waiting for another solution to be finalized and deployed.
- this also concerns many untranslatable names like brands (which are often restricted in the number of translations that they registered for specific markets) or people names (if they have several public identities for specific markets or specific uses such as romanizations of Chinese people name, which are not easily transliterable unless these people transliterated these names themselves and registered them to get some valid status for their travels abroad or their international business).
I think you misunderstood what these messages are about. They don’t translate the word “coordinates” (which should be translatable, as it’s likely to be different in other languages), but just the comma separator—just like MediaWiki:comma-separator from MediaWiki core, which is optional.