Excellent suggestion Iain! and I am surprised that after all our discussions on these areas that I completely forgot about Chad! It seems clear that areas of more extensive French presence colonially would more likely provide provenance for such a blade on a kaskara. These areas, in fact most of Africa, was a virtual hotbed of geopolitical colonial flux in the latter part of the 19th century.
It would seem that a poetic French verse, possibly from this esteemed French poet may likely have served metaphorically as an inscription on this French blade as well suggested by Yuanzhumin (superb job on that ttanslation BTW!
) . In all the political alliances, intrigues and conflicts of these complicated times of high adventure, this sword's blade presents some outstanding possibilities. It would be most daring indeed to suggest that the blade was in fact belonging to Rimbaud (1854-1891) however if he was as noted, one of the many arms vendors supplying arms in Yemen and Abyssinia it certainly strengthens the possibility of the words being his. Well placed and exciting suggestion Yuanzhumin!!
All the very best,
Jim