You can use Cloud Translation, it's a free and open-source project from Angry Monkey Cloud: https://github.com/angrymonkeycloud/CloudTranslation.
You should add a reference to jQuery first, then to the CloudTranslation JavaScript file:
<script crossorigin="anonymous" src="https://cdn.amcapi.com/translation/cloudtranslation-1.0.0.min.js"></script>
And add the configuration within the HTML head as follows:
<script type="application/json" id="CloudTranslationConfig">
{
"Settings": {
"DefaultLanguage": "en",
"TranslatorProvider": "Azure",
"TranslatorProviderKey": "{Your Microsoft Azure Translator Key}",
"UrlLanguageLocation": "Subdirectory"
},
"Languages": [
{
"Code": "en",
"DisplayName": "English"
},
{
"Code": "de",
"DisplayName": "Deutsch"
}
]
}
</script>
and add your own custom select (dropdown) having the class "CloudTranslationSelect" (you can customize the style of your select the way you want).
You can add your own translations to the configuration where it will reduce the calling from the translator provider.
More information found on https://www.angrymonkeycloud.com/translation