I finally figured out what was going on:
- I run MediaWiki 1.32.2 and the relevant HitCounters extension 0.3 (7638419).
- HitCounters 0.3 uses the global "viewcount" key which should be available from /wiki/languages/i18n/'<language>.json.
- Adding the "viewcount" key or "hitcounters-viewcount" to /extensions/HitCounters/i18n/<language>.json didn't have any effect in Hitcounters 0.3.
- Because I run multiple language instances of a wiki which share most files from a shared pool, I tried and edited the relevant strings in /wiki/languages/i18n/<language>.json. BUT - I had overseen that all localized wiki instances still had their own /languages/ folders.
- So I removed them and added symbolic links to /wiki/pool/languages/ in order to have all wiki instances use one shared folder.
Now everything works fine for me. I guess I have to adjust things once more when I update MediaWiki to 1.35 or higher. I stored the enhanced files for me like this:
da.json: "viewcount": "Siden er vist $1 gange siden 22. marts 2021.",
de:json: "viewcount": "Diese Seite wurde seit dem 22.03.2021 bisher $1 mal abgerufen.",
en.json: "viewcount": "This page has been accessed $1 times since 22 March 2021.",
es.json: "viewcount": "Esta página ha recibido $1 visitas desde el 22 de marzo de 2021.",
fi.json: "viewcount": "Tämä sivu on näytetty $1 kertaa 22. maaliskuuta 2021 lähtien.",
fr.json: "viewcount": "Cette page n’a jamais été consultée depuis le 22 mars 2021.",
is.json: "viewcount": "Þessi síða hefur verið skoðuð $1 sinnum síðan 22. mars 2021.",
nl.json: "viewcount": "Deze pagina is $1 keer bekeken sinds 22 maart 2021.",
sv:json: "viewcount": "Den här sidan har visats $1 gånger sedan 22 mars 2021.",
sw.json: "viewcount": "Ukurasa huu umetembelewa mara $1 tangu Machi 22, 2021.",
tr.json: "viewcount": "Bu sayfaya 22 Mart 2021 tarihinden $1 defa erişilmiş.",
As I am not familiar with Arabic, Farsi, Hebrew and find editing rtl texts in Ubuntu's nano editor rather difficult, I left those three languages for my wiki instances untouched so far.