It depends on your employer. International banks are present in all major cities. So English is mainstream. And you do not need to be in Tokyo for that. The most important thing is where your trading computers are. Plus mind that hft and algorithmic trading are not the same things. Hft is proptrading which is now mostly forbidden for large international banks by Volker rule.

Note that the HFT business is most competitive Amstersam, New York, and Chicago. These places are like Silicon Valey in terms of the people that circulate between firms and know each other. There are good firms in Asia but for the most part they’re not considered top tier in terms of technology or competitiveness.

It’s not uncommon to take an HFT trade that is competitive in the US or German markets and go around applying it to markets like Tokyo, London, Singapore, Etc. But the converse is not usually as successful.

So if you start in Tokyo, it might be harder to move up and out just due to more restrictive regulatory frameworks and less efficient markets there.