Remember Bill Gates got started writing a Tiny BASIC interpreter for the ALTAIR.
There are better languages around, but you can easily write an interpreter for a small language of your own, and it's fun and good experience.
Start with whatever language you've already got.
You probably want to keep it really simple, like for starters only have numeric variables, and keep the variable names to single characters like A, I, or X.
You can do arrays later.
For expressions, like (F-32)*5/9 a recursive-descent parser is easy to write and excellent practice.
You don't need to build a parse tree - you can just calculate the results as you parse along.
Forget functions/subroutines. You can do those later.
For control structure, if you wanted to be really minimalist, you could stick to IF and GOTO.
You can do the more structured stuff when you get more confident.
When you get something working, you can elaborate it in whatever directions you want.