‘!’ character prepend to the filter string, like below:
filter:’!’+languageOrigin
<select ng-model="languageOrigin" ng-change="updatePrice()">
<option ng-repeat="language in languages">{{language}}</option>
</select>
<select ng-model="languageDestination" ng-change="updatePrice()">
<option ng-repeat="language in languages | filter:'!'+languageOrigin">{{language}}</option>
</select>