That feels awkward because in German "ch" is a hard stop. In order to make the word "flow" I tend to gloss it instead of making it hard. I guess the key part that both you and DanF1220 is that it's got some "back of the throat" sound so it. Tricky tricky.
Go raibh maith agat!
I read two different descriptions that helped me. One said that K is a closed sound, whereas ch is an open version where you continue to blow air - I sort of started to get it from that. And then another one said, "make a K sound, but blow air across the roof of your mouth while you do it," and that one made it click. The actual K part of it is much softer, I think, because you can't get that full K sound without the hard stop.
Don't know if that will help you, but it helped me! I found this whole guide very helpful in general for trying to learn the various consonants, especially broad and slender: http://angaelmagazine.com/pronunciation/introduction.htm
The German ch is far from a hard stop. Only in the beginning of words, in southern dialects it is, otherwise it’s a so called fricative. After back vowels (a o u) it’s pronounced /x/, which is the sound that is to k as f is to p, and as s is to t : it is pronounced with the same tongue position, but instead of stopping the airflow completely, you let the air through and cause friction, resulting in an almost hissing or scratching sound.
Now, in German it’s a bit more complicated than it seems to be in Irish, because there’s the distinction between the ich-sound /ç/ and the ach-sound /x/ (which I’ve just described). Irish has, as far as I know, only the latter.
There is an explanation in the sections on lenition (https://www.duolingo.com/skill/ga/Eclipsis) and eclipsis (https://www.duolingo.com/skill/ga/Lenition). Unfortunately my brain just threw up its hands at that point and I just went with, "Move along and come back to this later after you've been doing it for a while to see if it makes more sense later on." Bit by bit, it does sort of start to make sense, believe it or not.
The explanations are at the bottom of the first page on a particular section, and I sometimes don't even notice them there until after I've done the lessons and am wondering just what's going.
This probably isn't the right place to suggest this, but I don't know where else to mention it. I hope once this is out of beta, there might be more exercises on lenition and eclipsis, like a part 2 the way there are with other sections such as verbs.
While I'm at it, I'd like to see more examples of the genetive, since the same sentences keep showing up in the review and I think I'd kind of just memorized them without reading understanding it all that much. I've read the explanation and it all seems very arbitrary and I keep waiting to see "except on the 2nd Tuesday of months that end with y".
Alternatively, if anyone knows of anywhere there might be some very repetitive exercises offered elsewhere online, that would be great.
Sorry for co-opting your question like this but, since you mentioned it, that's something I've kept meaning to ask anyway.
If den chailin (can't find how to add accent mark for the second last i) means .off THE girl'. Why is it lenited? I thought only feminine nouns were lenited after the definite article - 'an'. Cailin is a masculine noun. I may be missing out on something here. Would appreciate a comment or two.
Please read the other comments before posting an inaccurate comment about something that has already been clarified.
There is no typo - den can mean of or off depending on the context. The Englishs word "of" and "off" are both derived from the Middle English word "of".