Legal Question in Business Law in California

Contracts written in foreign languages are enforceable just as they would be if they were in English. If you wind up in court over this, you will have to give the judge a translation. Unless the defendant claims that you have translated it incorrectly, that should be the only consequence of writing it in Korean.

Note that there may still be other reasons why you would lose the case. Without more facts, I can't assess your chances.

Even without a contract, the items you mention - racks and mannequins - would be considered trade fixtures under California law, and could be removed by the tenant at or before the end of the lease. If trade fixtures are left behind when the tenant's right of possession under the lease expires, the tenant may lose the right to come back and get them.

I'd say you are a tenant and the person to whom you were paying rent is your landlord IF he had the legal right to collect any rent from you. A person might have that right by being the agent of the owner, or being himself a tenant and you therefore a subtenant.

Taking rent from someone without the right to do so may be a crime called "rent skimming."

The obvious answer is that if the parties can't resolve it among themselves, with or without the assistance of legal counsel, then you have the right to sue for breach of contract and damages. The language is not an issue, you simply have to hire a certified translator. If serious about hiring counsel to protect you in this, feel free to contact me.