Do I have to worry about delays in international trains? (UK, Belgium, Germany) [closed]

Unfortunately delays and cancellations are not uncommon. You have a bunch of options here.

It seems like www.trainline.com will allow you to book this. You still have to split it into two tickets: Stuttgart to London and London to Glasgow but it's with a single operator and so you will be rebooked for free on the next available train if you miss your connection.

Trainline also honors delays from certain income providers including the German ICEs. https://faq.trainline.eu/article/449-miss-train

Otherwise I would book this as multiple flex tickets.

Overall this will be pricey. A third options would be to simply fly and buy some carbon offsets to mitigate the environmental impact.

Firstly, this itinerary can and should be done on two tickets. One Stuttgart-London (from ~€60) and one London-Glasgow (from ~£50).

The Stuttgart-London leg will be guaranteed - so any delays will allow you to take the next train.

Assuming you get an "Advance" ticket on the London-Glasgow train (that limits you to a specific train), then as per Missed connection even if the connecting Eurostar was delayed you will be allowed to travel on the next available train. (If you get an Anytime or Off peak ticket then you will be able to board any train in any case.)

Edit: addressing Owain's point

With a CIV ticket from London-Glasgow, you would be legally covered to be able to continue your journey in the event of any delays. These tickets are hard to get. However, despite this, and similarly to the "Split ticket" scenario described in the link I posted above, the UK train operators are very unlikely to prevent you travelling on a later train if a well planned connection is missed due to another late running train service (including Eurostar).

See also:

• Delayed Eurostar arrival in London, going to miss my connection, what to do?
• https://www.railforums.co.uk/threads/missed-connection-due-to-late-runnig-eurostar-query.117260/

[With an advance ticket,] once the journey has begun. If the passenger is delayed and the rail industry [...] is at fault, [...], change to another train of the same company is allowed to get them to their destination with the least delay. This is irrespective of combinations of rail tickets held.

If you book this on one ticket you are in a good situation. The railways must get you to your destination, and must take care of you.

But even if you are not on one tickets there are certain rights you have. DB and Eurostar are both members of Railteam, and as such if you miss your connection in Brussel of Paris because the ICE was late Eurostar will put you on the next train with free seats. It is important however that in that case that you get an endorsement on your ticket from the ICE conductor. (That is a good reason to print out your ticket, and not rely on an app).

You could book this in two sections: Stuttgart - Paris with DB, and Paris - Glasgow with Eurostar (select UK as country)