Hello,
The administrative boundaries of the Islamic Republic of Mauritania 
have been updated several times over the last ten years, with OpenStreetMap now being very outdated.
The first-level administrative division (wilaya) has seen changes in the boundaries on the coast, affecting Inchiri, Dakhlet Nouadhibou, Trarza and the three wilayat of Nouakchott. For example, Inchiri is now bordering Nouakchott, which has annexed land from Trarza to include the airport and the small locality of Agnodert.
The second-level and third-level administrative divisions (moughataa and commune, respectively) are not displayed either, despite communal boundaries remaining somewhat stable over the years; and several new moughataat being created over the past few years.
These maps are now available thanks to the National Agency for Statistics, Demographic and Economic Analysis (ansade.mr) making a shapefile available at the Humanitarian Data Exchange with the licence CC-BY-IGO. I am already using the map on Wikipedia for boundaries.
I would also point out to ANSADE’s excellent database from their recent 2023 census, which includes every single locality (even under the communal level) and the location of virtually all schools, health centres and mosques of the country; available here.
The General Directorate for Decentralisation and Local Development (dgct.mr) includes in its website the legal texts of some of those changes.
The DGCT includes the very useful decree specifying the transcription of the names of every commune and moughataa in French/Latin, available here. This decree remains the sole legislative official reference of toponomy, as de facto government and societal use remains inconsistent in both Arabic (due to Hassaniya and other national languages’ phonetic differences compared to standard Arabic) and French. Using the official toponomy may help achieve some consistency on OpenStreetMap. I will link to the Arabic equivalent document if I find it, but until then ANSADE’s census database should help.
The State Gazette (available at msgg.gov.mr) should also include said decrees detailing the changes, especially now that the website was recently revamped to include every released from 1959. I am happy to dig on said legal texts if desired to link every change, but I think the shapefile should suffice.
I sadly do not know how to import the shapefile to OSM, so I am kindly requesting help with said process. I can help with the rest if needed.
Many thanks in advance! 