you will be able to change all the add-on phrases.

the layout in the screenshot is from advanced attachments add-on, you need to purchase the add-on to get that layout:

https://gvectors.com/product/wpforo-advanced-attachments/

after installing the add-on, go to Dashboard > Forums > Settings > Addons Tab > Attachments Sub-Tab and Change the phrases`

Attach Files

Or drag and drop it here.

Max file size %1$s (dont change %1$ )

My media

I don't have any solution for code to make the last part work ass needed, The reason is that this is more close to manipulation on the browser. I have found out that the language can be changed by changing the browser language.

The code doesn't seem to work as intended> https://prnt.sc/1uvrir3

Thanks

Insert the below CSS code in Custom CSS Code Field:

Thanks, Seems to work only partially: https://prnt.sc/1uvrir3

Even if I minimize the window it still shows like this 

1) it's "squashed" and not displayed fully

2) not translation even in your code?

Thanks

Posted by: @dk1616

1) Is the "choose file" / "no file chosen" translatable? 

Insert the below CSS code in Custom CSS Code Field:

input#wpf_file::-webkit-file-upload-button {
    visibility: hidden;
}
input#wpf_file::before {
  content: 'Type Your Contnent';
  display: inline-block;
  background: -webkit-linear-gradient(top, #f9f9f9, #e3e3e3);
  border: 1px solid #999;
  border-radius: 3px;
  padding: 3px 8px;
  outline: none;
  white-space: nowrap;
  -webkit-user-select: none;
  cursor: pointer;
  text-shadow: 1px 1px #fff;
  font-weight: 700;
  font-size: 11px;
}
input#wpf_file:hover::before {
  border-color: black;
}
input#wpf_file:active::before {
  background: -webkit-linear-gradient(top, #e3e3e3, #f9f9f9);
}

Posted by: @dk1616

2) I chose a long display name and it's running beyond the border,

Use the CSS Code Below:

#wpforo #wpforo-wrap .author-data {
    padding: 6px;
}

1) Is the "choose file" / "no file chosen" translatable? 

2) I chose a long display name and it's running beyond the border,

--- is there any CSS that can fix it and contain it inside? 
--- OR is there any code that will set the max no. of characters for the username?

Thanks

You're searching the wrong phrase,

In wpForo Forums > Phrases` search for " ago " phrase, and you will see " %s ago " phrase, wpForo's part is " ago ", " %s " is WordPress part, which will be set as WordPress Language.