Apart from that, what can I do to meet locals? (Also my apartment in Gundeldingen. So I am so close to the city center) My german is so bad right now and I know that it might be a disadvantage for me. I am looking forward to your suggestions.
Nothing written above is specific for Basel, but this is how you generally meet new people.
Indigo Fitness has a lot of expats working out at the gym, I met some nice people there
Basel Dragons Running Club has plenty of English speakers
Basel Rugby games are next to Gundeli and lots of fun / mainly English speakers attend. There is always beers/food/parties during and after the games.
B Yoga has all English classes - nice people go there, there are other yoga studios about town that offer English classes/opportunities to meet people
Also check out Centrepoint (here: https://www.centrepoint.ch ). It’s a very friendly, English-speaking international group that includes Swiss locals and offers lots of activities. In particular, Centrepoint holds a “coffee morning” every Friday from 10:30 to 12:30 where you can go to meet people and find out about Basel. Centrepoint is located above Barfüsserplatz, at Lohnhof 8.
Kudos rotblau for immediately starting on your German. I believe something like a Verein, as suggested by Islander, is much more useful to help you with that than some pub, whether the other guests are English speakers or not.
Well done on being proactive about meeting new people and learning German
Check out the Basel German Conversation Group, it has people with all abilities (some speak zero German / others more advanced), and they meet every Tuesday to chat and practice German.
https://www.facebook.com/groups/germanconversationbasel
Have fun!
Most districts in Basel have a Treffpunkt (meeting place or community centre), there are usually things like yoga going on, ours does a monthly Saturday lunch for a few francs and has craft and fleamarkets during the year, also little music events and a summer BBQ. There is one in the Gundeli you could check out.
I was a member of Centrepoint for a bit as I wanted to join a German conversation group. Purely personal experience, it wasn't my cup of tea and I felt like a fish out of water. It was a bit too cliquey for my liking and I didn't feel I was fitting into the group well. First to admit I'm uncomfortable in those situations. I'm 61 and actually felt I was too young for it, despite other members being much younger (still youthful in my head )
Generally, you will meet people in Switzerland, like all over, by being active and joining groups, whatever they are. In Switzerland, for most people, this doesn’t come for free and you’ll have to put in some work.
Do your best to find out what is going on in your neighborhood and join whatever groups there are…
Are you religious? Join a house of worship and go regularly to events.
Are you athletic? Try to find a team?
There are community centers in different neighborhoods. Go and see what is going on.
Do you have a dog? A lot of people get to know neighbors while walking dogs? Are you willing to get a dog? It’ll help.
Do you have a small child or children? There are tons of parent groups all over and people are generally much more open to meeting new people when their children are young.
Are you open to volunteering? Here is a link to coordinate volunteers supporting Ukrainian refugees.
I found all of the above in 5 minutes. If you are serious about this, start searching and get involved.
Even though you are looking for locals, your best bet will be other expats with whom you share the common expereince of moving to Switzerland and learning about Switzerland.