While there is not any set limit of the number of HREFLang Elements you can have in your pages, having many of theme defeats the purpose of much of the other page speed optimization you are doing. However there are reasons to use them in the page so please review our When to use in-page HREFLang Elements FAQ.
For example, the average country/language HREFLang element is about 80 bytes which is nothing in the big picture of the page.
However, if you have a site with 30 languages that jumps to 2.37 KB which is a lot of text to process that can be moved to an external file.
The big whopper site American Express has 94 entries on the home page that add 8.7 KB to the weight of the home page.
About a year after releasing the HREFLang Element Google released the ability to manage this with XML Site Maps. Note one of the reasons they did this was to help reduce page size and make it easier for large sites to manage them.