Hello here, using deepin 15.3 OS

its nice distro however im having trouble to run apt-get update or apt-get install anything.. also cant update system which is bad cuz I made fresh install and needs to be updated.

repos generated by deepin install not working at all..
I was trying to add different ones from deepin mirror list.
Found my country mirror so I added, but no success.
Its a bit better but speed get down to 31kb/s and then stop in the middle. I have tried several countries including germany UK greece Slovak Polish and always the same problem appear. update stuck in the middle of updating. basically I cant install anything.

any help for this? I even tried add debian jessie repo but same thing happening. speed gets suddently slow until it stops definitely.

Thank you in advance.

edit: im trying to add repository using: sudo add-apt-repository ppa:freetuxtv/freetuxtv-dev
and it says command not found. how is that possible? Before, I was editing /etc/apt/sources.list manually.

Two issues here:
1. Deepin 15 and later is Debian based, not Ubuntu based. Utilities found in Ubuntu but not in Debian will be missing. This is to be expected. THere are flaws in the recent Deepin, and this video about fixing may help: https://www.youtube.com/watch?v=wFMZCNle7Bo
Cut to the chase: updating with the GUI interface and utilities may not work. Looking up and manually updating your list in the terminal interface (vi much?) should solve that issue. By this I mean manually editing the sources without using the apt utilities.

2. IF that does not resolve your issue, it is possible you have some other system or network issue throttling your updates. After you fix your lists, return and report what you did and what the results are and we will try to answer any remaining questions.

to be expected if deepin 15 is indeed based on debian, because that's a ubuntu specific command.
and don't use ppa:s on debian, anyway.

Thanks for reply. Yes I have followed the video of course. I have installed several machines in the past and this video helped to set things right.
But now its terribly slow when running apt-get update doesn't matter which mirror I use. Even internet connection itself is broken somehow,
Firefox loading and downloading files strange. i have fast internet connection and downloading jump in 5 mb, 10 mb then stops, wait 10 seconds
and then it continue normal speed and then again stops and wait for 10 seconds.. this way I cant really install/download anything.
I have internal Intel wifi card and external alfa awus036nh. both works just fine in Kali or any other distro. I have given up and replace deepin with different linux but you could still help me as I would love to come back to deepin in case this problem could be solved. thank you

PS: I would not run apt-get add repository I know its from ubuntu.. But you have to understand I had to try everything in my situation even it might not make any sense.

That sounds much like something is mucking up your networking at some level. Perhaps name resolution. I have seen that behavior when there was a speed mismatch on a physical NIC port, but never on WIFI.

Have you tried disabling IPv6? If it is not required, it can mess up several network related things and this sounds like a common IPv6 complication.