Steps to reproduce the issue

Download Joomla_4.2.10-dev-Development-Full_Package.zip from Nightly Builds.
Install Joomla 4.2.10-dev. Select language English (United Kingdom).
The installation is completed normally.
Check the database table _finder_terms_common that it has 174 rows.
Go to System - Languages and click Install Languages.
Install Dutch (nl-NL), ignore the info "Language pack does not match this Joomla version. Some strings may be missing and will be displayed in English"
The message "success -
Installation of the language pack was successful" is displayed.
Check the database table _finder_terms_common. (1)
Download the German language pack from https://downloads.joomla.org/language-packs/translations-joomla4/downloads/joomla4-german/4-2-9-1
Go to System - Install - Extensions - Upload Package File.
Select the German language pack that was downloaded.
The message "Installation of the package was successful" is displayed.
Check the database table _finder_terms_common. (2)

Expected result

(1) more than 275 rows
(2) more than 1266 rows
The file com_finder.commonwords.txt in the Dutch language pack has 108 words, some of them duplicated.
The file com_finder.commonwords.txt in the German language pack has 992 words.

Actual result

(1) 174
(2) 174

System information (as much as possible)

Joomla 4.2.10-dev of 27 March out-of-the-box
PHP 8.1.16
Wampserver 3.3.1 64-bit on Windows 11

Additional comments

Joomla! Forum topic common words in dutch are not blocked