The Multilingual version of this mod contains translations for all Fallout 4 supported languages, but google Translate was used so they will be 'basic!!'.
You can create your own updated translations, that will override the ones in this mod, quite simply as follows:

You need some programs for this. They are not part of Fallout 4 so can be unzipped anywhere.

Fallout4Translator (latest version is "xtranslator") - Fantastic program for creating translations.

Currently here are only 4 translation files you need to replace for your language, 2 for Flyable Vertibird (FPVertibird) and two for the main part of Hotfix 5 (FPV_Armored) extra patch.

You will be updating the following files in your Fallout4\Data\Strings directory (to override the ones built into this mod).

FPVertibird_xx.STRINGS
FPVertibird_xx.DLSTRINGS
FPV_Armored_xx.STRINGS
FPV_Armored_xx.DLSTRINGS

where "xx" is your language, e.g. Fr is French.

Step 1: Get the latest "english" (En) version of these files - they are in the mod kit under FPVoptions\Strings and copy them into your game's data/strings directory.. If there has been a subsequent update/hotfix then you will instead have to extract them from that update's replacement FPVertibird - Main.ba2.
(For that you need the Archive2  program from the Creation kit, or one of the BA archive extractor programs fround on nexusmods).

You need to ALL the english Strings files - even though only the above need to be modified.

Step 2: Now you need to do the same for the string files for your language. However, if there have been better versions already created (either by yourself or another Mod author), then all you need is those.

Step 3: Install and setup xTranslator (you will need to configure it for your language and game files location). See documentation on that mod.

Step 4: Run xtranslator.exe and select "Options" "Dictionaries and Languages". Change "Source Language" to ENGLISH and "Destination Language" to your language. Click "Ok".

Step 5: Now choose "File" "Load Strings" and select FPVertibird_en.STRINGS. This will load in the English string files (you extracted). If all goes well there will be 246 STRINGS and 77 DLSTRINGS (V1.6)

Step 6: Now choose "Tools" "Load .strings as translation" and select your language strings file FPVertibird_xx.STRINGS. Set overwrite  as "Everything". You will now have the English lines on the left and your language translations on the right.

Step 7: Now go through the various lines in your language and modify the ones that have a bad Translation.
NOTE: DO NOT change the special sequence %.0f you will see it in some lines - this is used by the game to insert numbers at that point.

Step 8: Now choose "File" "Finalize Strings" and confirm you are overwriting. This just updates the STRING files for your language, the esp files won't be touched as they do not require modification.

Step 9: Now repeat the above process for the Hotfix (currently that is Hotfix 5, which uses  "FPV_Armored_xx.STRINGS").
Note that FPV_Rings is no longer used so no need to touch it.

You are done! Run the game and enjoy your (better) stranslations!

Extra: MCM menu

The MCM menu also automatically uses the correct translation for your Game's language.
These translation files are kept under your fallout4\data\interface\Translations directory and are of the form FPVertibird_xx.txt.
These translation files are just unicode text files (one for each language) so can be edited  by the method of your choice.
xTranslator support editing them via "file" "Load MCM/translate file" but notepad will work.
Do not touch the variable starting $FPV but the text after the tab is what you see in MCM.

It would be very nice if you contacted the Author and offered your updated STRINGS files for inclusion in the mod so everyone can benefit.