changing the language of error message in required field in html5 contact form

I am trying to change the language of the error message in the html5 form field.

I have this code:

<input type="text" name="company_name"  oninvalid="setCustomValidity('Lütfen işaretli yerleri doldurunuz')" required /> 

but on submit, even the field is not blank, I still get the error message.

I tried with <input type="text" name="company_name" setCustomValidity('Lütfen işaretli yerleri doldurunuz') required />

but then the english message is displayed. Anyone know how can I display the error message on other language?

Regards,Zoran