In 2003, I was involuntarily hospitalized because my parents thought I was mentally ill.
I talked with my psychiatrist and she said I have the symbolic thinking, because I can speak in both Chinese and English.
In symbolic thought, I would look some English words and Chinese characters in the same way.
For example, my English name is Walter, it has the same pronunciation with water. Also, I would look English words such as good, ground have something to do with God, because there are the three letters g o d.
Now, I don’t think symbolic thinking is the symptom of mental illness. Some people without mental illness Also have the symbolic thinking.
I think you are correct that it can happen to people who are not mentally ill. Especially while learning another language. I had two Chinese friends in college. One went by the name Doria here so it would be easier for people to pronounce her name. I remember her mentioning that for her to pronounce the name Doria she remembered the word Dollar. My other friend’s name was Quan and he too had some words he’d use that would remind him of others. My mom who also had to learn English sometimes practices saying Washington when she’s going to use words with the W sound because that sound rare in Spanish. That might be a little different though.
As for the symbolic thinking you mentioned. I have heard of that as a symptom too. I forgot what it is called. Some websites describing symptoms have used this example, sometimes when the word “psychiatry” is heard, a person who suffers from schizophrenia might instead hear, “Say Kaya tree.” And associate in with something more mystical in nature. I know that type of thing can happen when a person is not taking medication.