Best plugins to make your site more flexible and responsive

Hello guys!

The website is nothing with out extra functionality and flexibility. So for that purpose we go for some extra plugins but still there are so much you need to do and still there are not much best plug-ins you found.

I have two options now,
1 - Go for developers
2 - learn myself but it will take much time

I can not hire a developer now. Because they create a back door which is harmful for my site future.

Moreover, i have some plugins installed into my site.
1 - Insert header and footer
2 - WP rocket
3 - Updraft plus

These plugins I have installed into my site. by the way you can check slinger machine site here and suggest me accordingly.

What are those plug-ins which will make my site to show different languages into different countries?

How to make a site show multiple button colours on the basis on light.

I would like to know what are those plugins which made your site more flexible and nice.