Following a discussion with Breton Wikimedians on Freenode #wikidata-fr, the namespaces and magic word could be translated like this:

Were also considered to translate invoke during the brainstorming session:

• aspediñ, used as invoke, but to invoke gods/deities/spirits
• gervel, provided by Ofis, which is the verb at the infinitive for the radical galv, see also this dictionary entry

Have submitted these translations @Ash_Crow and @VIGNERON