This functionality is included in Lightning 2.9 by default. Having it installed and enabled in 2.9 or above can cause conflicts, please uninstall.
In version 0.4:
Lightning localization is used for menu entries and buttons as well as for patterns to find dates and times. You can pick specific locale for detection or let it detect email language automatically based on dictionaries enabled. In cases when email contains more datetime information than needed you can select the appropriate part before conversion to improve detection.
In version 0.3:
The context menu items are in English on purpose.
Supported locales for date and time detection include en-US, et, sv-SE, fr, de, zh-TW, es-ES, sl, eo-EO, eo-XX, hu, ru, it, gd, ja and ca. To detect languages other than application locale you need appropriate dictionary installed and enabled.