The first Hacktoberfest problem that I have been involved in is helping translate the Trail-Sense project to Vietnamese.
Trail-Sense is an application for using Android phone sensors to assist with wilderness treks or survival situations.
The owner wants to translate the Setting of the app to many languages to make it more user-friendly. The issue has been discussed here.
It has not taken me a lot of time to work on the issue since the owner takes advantage of the Weblate platform. The platform is easy to use, and it can track the progress of your translation.

The project owner was helpful, and he explained what he expected and what I should do to the issue. So, in overall, I don't have a lot of difficulty working on this issue.
I think it is a useful project, and I am happy that I can contribute a small part to it.