the international unit for 1000 is "kilo" (k).
This unit is not being used properly by ahrefs.
In the keyword explorer I see the volume of "38K" in English and in German "38T". I suppose the "T" should mean "Tausend".
Actually, according to ISO and SI, it should be "38 k" in both languages.
Since the internet is international I would suggest to stick to international standards and the SI:
This will also save you some time and work developing your tool. Less coding and less translation.