French translation not usable: contribution proposal

[audour]

French translation is not usable (too many mistakes/missing translations)

For instance within superset/superset/translations/fr/LC_MESSAGES/messages.json

• "Annotation delete failed.": ["Annotations et couches"] -> it means "Annotations and layers"
• "Annotation layer parameters are invalid.": ["Les couches d'annotation sont toujours en cours de chargement."] -> it means "Annotation layers are still loading"

Contribution proposal

I've created this issue to avoid effort duplication by informing other potential contributors that I'll propose a PR for an improved French translation for Superset 1.3.0 during September 2021.