Question

can intake of carbonic acid and citric acid simulataneously form poison

Answer 1

There is no reaction between carbonic acid and citric acid.

These two weak acids have similar dissociation constants in water.

A low Ka indicates a relatively small number of acid molecules will form an anion stabilized by water. Two weak acids with similar dissociation constants will coexist in a solution without interacting.

If two weak acids have very different Ka then there can be a reaction.

In this case nothing would happen.

So, you can safely drink your Coca Cola after you have put some lemon juice in it.