Please help us help you and fill where relevant:
Your LimeSurvey version: limesurvey5.2.6+211213
Own server or LimeSurvey hosting: Own Server (Windows 2012 Server, running on IIS 8
Theme: Bootswatch Theme ( bootswatch)
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Hi - firstly, thank you for creating such an amazing product, for free!

Secondly - I am currently uploading limesurvey5.2.6+211213 to my site, and it takes up 280 Mb and contains 20,345 files.

I wondered if there is any way I can save space on the server by being able to safely delete unused components or files?

For example, I notice that the "tmp" directory is 63Mb in size and contains 6,000 files.

If I'm only using English, can I delete contents from locale for other languages?

Probably there is no way to safely do what I'm asking without breaking the whole thing, but I just thought I'd ask anyway, out of interest.

Thanks

tmp directory can be reset each night : github.com/LimeSurvey/LimeSurvey/tree/master/tmp
Because it was not included and copied again and again.Maybe it's assets directoy ?

Yes you can delete whole po file.
You can delete theme/surveys/ except vanilla
etc …

But you never get a light system …

As Denis says, you can delete certain parts like the non required PO files, etc., but you will probably gain very little.

But today, 280MB is nothing. Some years ago, OK, webspace often hat little storage space, but this shouldn't be a problem today. Keep in mind that if you have a lot of respondents and big surveys, the sessions files might (temporarily) need quite a lot of space as well. So if the 280MB are already a concern, you might want to look into this as well.