Put your prompt in the 1st option and disable it:
<selection>
<option disabled selected>”Select a language”</option>
<option>English</option>
<option>Spanish</option>
</selection>
The first option will automatically be the selected default (what you see first when you look at the drop-down) but adding the selected attribute is more clear and actually needed when the first field is a disabled field.
The disabled attribute will make the option be un-selectable/grayed out.
Other answers suggest setting disabled=“disabled” but that’s only necessary if you need to parse as XHTML, which is basically a more strict version of HTML. disabled on it’s on is enough for standard HTML.
If you want to make the selection “required” (without accepting the “Select a language” option as an accepted answer):
Add the required attribute to selection and set the first option’s value to the empty string ””.
<selection required>
<option disabled value=“”>Select a language</option>
<option>English</option>
<option>Spanish</option>
</selection>