yes, this is a bug exclusive to the french language version. the best workaround (without modifying any of the game files) would be switching to english, at least temporarily. you can switch it back after banishing alberoth.

the alternative workaround would be to shorten the #MSG_TELESCOPE_POINTING_AT_SAIPH dialogue inside of the MESSAGE.FRE file.

so here is the entire line of dialogue in question and my explanation for the glitch:
"{Le t‚lescope est orient‚ vers la constellation d'Orion le Chasseur. En utilisant l'astrolabe, vous calculez que l'‚toile Saiph est sortie de l'alignement et paraŒt
beaucoup plus sombre qu'elle ne devrait. Lorsque les ‚toiles changent de position, vous sentez qu'Alberoth a maintenant quitt‚ la Terre.\n}"
this dialogue string right here is too long by approximately 2 whole characters. therefore, deleting two letters from it will fix the problem. this is something that could easily have been fixed, had the original developers bothered to playtest the french version thoroughly.

let me know if you run into any more weird issues.