> For starters it appears to be impossible to even trade in foreign bonds with traditional brokerage accounts in the United States (hosted by E-trade, Morgan Stanley, Charles Schwab, etc).

Try Interactive Brokers. They are US-based, but offer accounts in most other countries. (Insane list here: https://www.interactivebrokers.com/en/accounts/open-account-...) I frequently recommend them here, so much so that I must look like a shill. I assure you that this is not a sponsored post! I have been a customer for 10+ years. I describe their service as institutional in breadth, but offered to retail customers. The number of international stocks markets, futures and options markets, and fixed income markets (all types of gov't and corporate bonds) is stunning. The numbers look similar to a Tier 1 investment bank, like Morgan Stanley, could offer their institutional clients. It is unmatched for non-institutional (retail) traders in my experience. It also has crazy low fees and is wildly transparent about them. To me, the only negative point is the website is a bit slow and feels about 5 years out of date, but that's not a deal breaker for me. I can trade all equities on the website, and the more complex things (like bonds or futures) I trade using their (I assume white-labeled) Java trading app that is cross-platform.