Does a site/page get a penalty for spelling mistakes?
Also a spelling mistake could be a unrecognised brand name so that is not really a spelling mistake and so on.
No.
There are only two possible ways it could be a penalty:
- Your readers/clients think it looks sloppy and unprofessional.
- You misspell a keyword and it counts against you.
However, if you misspell something on purpose because it’s a brand (like Symfony), that’s fine.
By penalty you mean SEO penalty right? I don’t think it would have a direct penalty. However, having a lot of spelling errors can give your readers an impression that you aren’t professional, which in turn can increase your bounce rate. Since bounce rate is rumored to be an SEO signal, then having spelling mistakes can indirectly affect your rankings.
Which is the most important reason NOT to make such mistakes and/or correct them as soon as you are aware of them. The rest? Not so much.
Though as Google keeps telling us “Write for people, not for search engines”
I guess there should be a penalty but not that big a penalty.
I have seen spelling mistakes even in Ads displayed on google thru google adwords.
Regards.
Spelling mistakes are harmful for ON page SEO specially . So try to avoid it .
That is not the reason one should avoid them. It should be done to make the reading experience easier for whomever may be reading. Which in turn keeps them coming to your site.
But besides that, this is not the SEO forum and we won’t be discussing that here. So lets keep on track please. 
Since a reader certainly can’t penalize a page except by leaving it, I am assuming the original question was about SEO and not adding content for people.
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