Obviously the literal, word-for-word translation of, "yet another leg to stand on" sounds odd, but that isn't to say that the average English speaker wouldn't know (or could guess) what you meant.

However, because there isn't an idiomatic equivalent (at least not one I can think of off the top of my head), I think you have to be a bit more creative and take the context into account. If I've understood the context correctly, this is advice from a lawyer to people wanting to dip their toes into the world of car sales as a side hustle. Because a person can have multiple streams of income, I feel like you could play around with "add an additional income stream" or "diversify your income streams".

If you wanted to get away from the "side gig"/financial aspect of the expression, you could try something along the lines of "add another skill to your repertoire", given the person would have to learn the ins and outs of car sales.

If you want to keep it neutral: "another tool to your toolbox".

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Note added at 19 hrs (2023-05-27 16:36:38 GMT)
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Forgot to include my reference! After reading it through, it looks like the article is about car/body shops wanting to diversify their business and starting selling used cars.

https://modernaverkstaden.se/bilforsaljning-ytterligare-ett-...

“…” depending on further context.

“It never hurts to add another income stream to your repertoire.”
https://www.instagram.com/p/B-xrh47pgmi/

This is the classic phrase for this, or Adrian's suggestion. However, as it is relatively ancient in origin, maybe a considerable proportion of potential readers of the text will not know this phrase. In that case, "another tool to your toolbox", as suggested by Andrew, also would work well.

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