It's good to learn that you are good at several technologies. (But don't think I am praising you. In English, people always try to say positive things to make you happy.)
If you want to be a system admininstrator, you need to improve your English, which is a big challenge. It will take you a long time to get a System administrator because the market requirement is small. Once you get a job, it is quite stable. If you are laid off some day, it will take you a long time again to hunt for a now job. AS/400 is still in use but it is not as popular as Unix. Oracle DBA is welcome but there is a big pool of candidates. I think the most important thing for you is English. For immigrants, nothing is more important than English.