This is somewhat related to the problem in T252277: columns are sometimes too narrow for some types of content, especially for tables. But this task suggests a different solution. Both can be implemented some day.

The proposal here is to make the columns resizable. Currently, the three columns —source, target, and tools— are of equal width by default. It would be nice to make them easily resizable by the user.

This was suggested at https://nl.wikipedia.org/wiki/Wikipedia:De_kroeg/Archief/20200410#Feedback_vertaaltool :

Ik word gedwongen in drie kolommen te werken, (1] Engels 2] Nederlands 3] foutmeldingen, gereedschappen en waarschuwingen) zonder dat ik de breedte kan aanpassen. [...] Er zijn verschillende oplossingen denkbaar: [1] kolommen die je naar behoefte breder en smaller kunt zetten, zoals bij een spreadsheet en veel webpagina's; [...]

Google translation:
"I am forced to work in three columns, (1] English 2] Dutch 3] error messages, tools and warnings) without being able to adjust the width. [...] There are several solutions imaginable: [1] columns that you can make wider and narrower as needed, such as with a spreadsheet and many web pages; [...]"

Resizable page sections exist on comparable websites, for example https://jsfiddle.net/