It will be useful to give guidelines for taking good screenshots.
For web browser screenshots
Use a browser extension like Window Resizer (not necessarily the best, just the first result) to keep a consistent size.
Either use the build-in developer tools (F12 on Linux or Windows) and the 📷 button, or a screenshot browser extension to take the screenshot. Or Firefox has a new built-in screenshot thing: https://screenshots.firefox.com/, it looks like this makes it very easy to screenshot a single element of a page (e.g. a dialog) so there's no need to crop afterwards.
For other screenshots
Use the correct shortcut to take the screenshot. Especially on Windows and Linux, there are shortcuts to screenshot only a single window, which saves cropping: https://www.take-a-screenshot.org/windows.html
There are also tools to resize windows to specific sizes
Both
Investigate whether it's better for screenshots to be taken at 2× resolution, so they don't look fuzzy when shown on HiDPI screens.
Investigate how the screenshots are scaled in the created document
Automation
It would be possible to automate the screenshots, for example to re-run all the screenshots with the tool set to a different language, but setting up and maintaining this is probably more work than is reasonable.
It will be useful to give guidelines for taking good screenshots.
For web browser screenshots
For other screenshots
Both
Automation