Hello dear fellow LingQers!
I would like to listen repeatedly to a specific sentence, in slow speed.
Also I would like to listen to a random part of a text (only two words, three sentences together, etc) repeatedly in slow speed.
How can I do that?
Best greetings from Germany!
When you playback the audio of a text you can set audio speed by pressing the field “1x”. You can do so several times to switch through the different playback speeds. There is also a button for karaoke mode, in which the sentence currently read is hilighted. Clicking on a sentence there will let the audio jump to that sentence, which is the closest you can get to repeating single parts in lingq as far as I am aware of (not a long time user, though, so I may have overseen it).
If you want to listen to specific parts several times the best approach probably is to download the audio and modify it to your likings in a program like audicity.
Besten Gruß zurück.
Thank you very much for your reply! Vielen Dank! 
I will consider the support with an “external” software like Audacity.
I wonder if the functions that I mentioned may be developed in the near future.
The devs are reading the forum, although it might make sense to shift the topic to the support and feedback subforum (you can do so by pressing the icon next to the thread title).
Just random thoughts. You could also try some Chrome extension to see if there are already something that does this job. For example, Reverso extension allow you to highlight any part of the text and TTS it.
If you use VLC, it slows down quite well an audio file with more precision but you need to cut it at your desire as @Obsttorte suggested.
If it’s a Youtube video you can use Language Reactor that does a very good job at this.