What is the origin of BSO - and is it internationally recognized?
In German, I have never heard anything similar. I think one reason is that everyday cycling is more common and many people have a cheap, battered bike to get to the railway station or the local shop, so you could argue that most bicycles you see in town would be seen as BSOs by UK cyclists. It doesn't make sense to invent a new term for something that is common and already has a name.

When you observe bikes in town, in the UK (where I live now) you can rather clearly see two distinct groups: high-end bikes for the sports market (and people dressed accordingly) versus really cheap ones (often students in uni towns). In Germany it's much more a continuous spectrum with a lot of middle ground of various urban bikes, so it would be difficult to draw a boundary.

Most people buy bikes in the local bike shops, but shops tend to have a wide variety from cheap, simple, factory-built ones to high-end custom-built, so the fact that they are sold in LBSs isn't necessarily a criterium for quality or price.

Another factor is that "BSO" is a term that is a bit arrogant and derogatory, sends the message: "You are not doing it properly", which is what bike advocacy groups really want to avoid. In Germany, cycling is very much seen and promoted as everyday activity, and the cycling groups want to avoid terminology that would people off. It's better if people cycle on a cheap bike than not cycle at all. It's possible that the cycling sports community in Germany has derogatory terms for non-sportists, but I don't think it's common outside. Again, in UK the community is different and more sports-oriented (although that's beginning to change, in the last 5 years or so).