Any invalid URLs should serve a "410 Gone" error with a message informing the user that the page they are requesting no longer exists, and with links to the top-level site pages. How you do this depends on your stack.
You could set up a simple database, JSON file, or any key: value scheme, such that when an invalid URL is requested, the server ...
Either way can work fine for SEO. There is going to be no difference in crawl rate. Targeting can be done either way with hreflang. I have a site with great SEO with English at the root of the domain but subdomains for every other language. Wikipedia (which also has great SEO) uses a language subdomain for every language including English.
The presence of a Human-readable URL affects the ranking of multilingual website in search results.
If the translation turns out to be wrong and is already indexed by spider
Based on official guidelines, don't use the robots.txt file for canonicalization purposes.
You can blocks sessionid URLs using Parameter Handling
If you block using robots.txt, you may lose the search ranking signal from the link to your URL with sessionid/params.
These pages are not a good fit for Google AdSense. You can try to put AdSense on the pages, but AdSense is probably not going to populate the ads very often and the ads are not going to convert well.
When you put ads on a page (URL), the Google Adsense crawler comes to visit the page to see what content that page has on it. You will see a hit in your ...