Can I sue for retaliation ?

Maybe retaliation, IIED and constructive termination.

Can I sue for unpaid overtime

Yes, if you are non-exempt and making double minimum wages. OT for 8-12hours/day and 2 OT for 12+/day and OT for 40+hours/week, etc. Buying lunch...

There are already some really good answers but you need to contact an employment attorney right away. You want to make the right moves at this...

Yes. You are entitled to at least minimum wages. You could be entitled to waiting time penalties for up to a month pay. However, the case might...

Can I get a work permit even though I'm undocumented ?

You don't have to be documented to work. You are still entitled to the rights and protections under the CA Labor Code. If you're referring to a...

Do I have to download a messenger app on my personal phone for work if my boss asks? Can they fire me if I don't?

I think your employer may fire you under these circumstances. CA is at-will employment. However, if you're required to communicate with your...

Can a company take away future pay from human resource manager's past miscalculation of paternity leave?

Your employer can't take away 1-2 paychecks based upon these circumstances.

Can my employer fire/demote me for the person I replaced when they quit?

CA is at will employment meaning your employer can let you go anytime. It does not sound like retaliation or wrongful termination.

Do I have any legal rights when it is clear that my boss is working to replace me with someone that speaks another language?

Great answers above. You won't know for certain until you speak with an employment attorney on CELA.

Since it is at will employment, burden is on you to show wrongful termination and I don't think it's there with those set of facts. It is not...