BO -> Product -> edit prodcut -> Tab Pricing
The field unity near Price per unit (tax excl.)
Quote<input type="text" id="form_step2_unity" name="form[step2][unity]" placeholder="Per kilo, per litre" class="form-control">
it is not translatable.
This field is not visible in the front end template.
Tested in versions 1.7.5.1 and 1.7.6.1