in /media/vendor/choicesjs/js/choices.js we have this code

  _proto.setWidth = function setWidth() {
    // Resize input to contents or placeholder
    var _this$element = this.element,
        style = _this$element.style,
        value = _this$element.value,
        placeholder = _this$element.placeholder;
    style.minWidth = placeholder.length + 1 + "ch";
    style.width = value.length + 1 + "ch";
  }

For example it defines the min-width and width of the input in the tag field.

When the placeholder text is long, the min-width may be too important, forcing the field to go over the edge of the page.

Steps to reproduce the issue

Install Persian language although the issue is NOT related to RTL.
Edit an article and look at the Tags field.
Switch between en-GB and fa-IR (Persian)

en-GB
The placeholder string is
JGLOBAL_TYPE_OR_SELECT_SOME_TAGS="Type or select some tags"

Which gives for the input field

The element values are:

fa-IR
The placeholder string is
JGLOBAL_TYPE_OR_SELECT_SOME_TAGS="برخی از برچسب ها را تایپ یا انتخاب کنید"

Which gives for the input field

The element values are:

The only way I found to partly correct this issue without touching at the js is to override the min-width.

For example in choices.scss:

.choices[data-type*="select-multiple"] .choices__input, .choices[data-type*="text"] .choices__input {
    padding: 0.2rem 0 0.356rem;
    color: #495057;
    min-width: 35ch !important;  // added
}

It still limits the number of characters as placeholder

For Persian the alignment is not too bad

the default for German is already 35ch (and still not perfect alignment for German)

Anyway in all cases, when reducing the window width, it is always bad... (until we get to x mobile view where all fields are 100%.

@ciar4n