Building a garden wall - materials and procedure?

There are such kits, they are quite expensive... theoretically, old stones do actually work, but you already mentioned the transport.
Just like in NDS neighborhood law for trees. As far as I know.

I had also seen those kits, they look nice – but are definitely too expensive for me. I would rather cobble it together from cheap standard stones.
But if you really have to dig 80 cm for it, I think I’ll probably leave it and take the fence instead. :(

Not necessarily as pedantic as Google says. The problem is that after several winters the wall could simply collapse because the ground gets moist and could cause damage due to frost. It took our three people a weekend for our wall, which is about 10 meters long. We got a concrete mixer from the neighbor and cement came along with the stones. Then two small trailer loads of gravel and off we went.

I don’t think I’d want to build that long a wall anyway. Can it really collapse? Where are the stones supposed to go if there are more stones underneath? I somehow can’t visualize what the weather could do to the wall.

I don’t know what Google says, but for a 150 mm wall and bigger (and not knee-high) I would maintain the frost-free 80 cm base.
Otherwise, it could quickly topple over.

Yes, that is actually what I’m afraid of, especially if I want to build it near the property boundary. I don’t want it to topple in the wrong direction and demolish the neighbor’s corrugated metal shed. :D
Although I would also want to build it around the corner – sort of rounded. Similar to the photo, so not the same height all around, but with the highest part at the shed (max. 1.80 m) and then sloping down towards the end.

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I have an animal-like urge to do some masonry.
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And that coming from the mouth/fingers of a woman. You are surely welcome at any construction site if that urge doesn’t subside :)

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a few square meters of facing bricks
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Square meters = Quadratmedder or Quadratmeddder (with emphasis on the "dd/ddd")
Then it sounds more (casual) like a construction site

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the ruin look of the photo is visually desired.
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Maybe has some of her wall to spare? As far as I remember, there are also a few Roman muscle-bound gladiators with wine standing around.

I had also seen the kits, they look nice – but they are definitely too expensive for me. I would rather cobble it together from cheap standard bricks.
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see above
Or: if rubble stone is also an option, I would ask at a quarry :)
(relatively spontaneous thought ...)

No way. The wall stays

Demolitions
Excavation
Stone collection sites

I also saw the kits, they look nice – but they are definitely too expensive for me.

At least in our area: Classifieds! The beautiful old bricks for about 1 euro each top any pseudo-vintage stuff. A good foundation ensures (as written above) durability. Although "back in the day" it worked with significantly less. It surely depends on the region and the harshness of the winters. And then get started! You can google a few basic things to keep in mind. But especially with your project (where it’s not strictly about energy regulations, statics, or architectural style) you shouldn’t stress too much. Just do it, it will be very good!

for roundabout 1 Eur/piece

Unfortunately, mostly including mortar (which is not exactly cheap either, especially if you buy it little by little in 20kg bags from the hardware store due to lack of storage), quite an expensive affair. I once bought up all the small granite stones in a clearance sale at a furniture store with a garden center... went there 3 times, almost wrecked the car, then bought mortar and built a knee-high bed edging. Without a base and such. That was no small feat! Best done with a trailer to a demolition house ... :)

At least in our area: classifieds! The nice old bricks for around 1 euro each beat any pseudo-vintage stuff. A good foundation ensures (as mentioned above) durability. Although "back in the day" it also worked with significantly less. It surely depends on the region and the severity of the winters. And then get started! You can google a few basic things to keep in mind. But especially with your project (where it doesn't strictly follow energy regulations, statics, or architecture) you shouldn't get too worked up. Just do it, it will be very good!

Wow, 1€ per piece is definitely more than I want to spend. :D Or rather the upper limit. In the meantime, I just looked for new clinker bricks, in a somewhat rustic look (which we also used for the house). That would be doable price-wise.
For the foundation, I also asked a master bricklayer from the neighborhood, who saw it similarly to you. Of course, you should actually build frost-proof foundations, but for a garden corner like this, that would be overkill. He said if it really gets down to -12°C outside for several weeks and the ground freezes that deeply, the wall might suffer a bit / sink, but should you really expect that? He said I should dig a bit, put in concrete, and then just get started.

Unfortunately, including mortar (which isn’t exactly cheap either if you buy it in 20kg bags little by little from the hardware store due to storage issues), it’s quite an expensive affair overall.
I once bought up all the small granite stones at a furniture store with a garden center during a clearance sale... went there three times, nearly wrecked my car, then bought mortar and built a knee-high bed edging. Without a base and all. That was no joke! Best to go to a demolition house with a trailer... :)

I haven’t even checked what mortar costs. We have a building materials supplier (which is also quite cheap) within walking distance. I was planning to buy from them because I think they can deliver it for little money.
Does your bed edging hold up well without a base? If it’s only knee-high, nothing much can happen, right?