Final answer:
Bulgaria, Serbia, Albania, and Croatia are four out of the six countries along the Danube River route that have English-language names ending in 'A'.
Step-by-step explanation:
The countries along the journey of the Danube River from the Black Forest in Germany to the Black Sea in Romania that have English-language names ending in 'A' are:
- Bulgaria
- Serbia
- Albania
- Croatia
These are four out of the six countries.