The control is named VariationsLabelMenu and resides in the 15 hive (Same as for 2010 in the 14 hive), C:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\TEMPLATE\CONTROLTEMPLATES\VariationsLabelMenu.ascx
By default this control is hidden and if you are using a custom master page it might not been added to the master page. In that case you can use following markup in the master page to add this control.
<!-- Register dll -->
<%@
Register
TagPrefix="PublishingWebControls"
Namespace="Microsoft.SharePoint.Publishing.WebControls"
Assembly="Microsoft.SharePoint.Publishing, Version=15.0.0.0, Culture=neutral,
PublicKeyToken=71e9bce111e9429c"
%>
<!-- Add control and datasource -->
After the Div with id suiteLinksBox add below code in your master page :-
<div
id="LanguageChangeControl">
<cms:VariationDataSource
id="LabelMenuDataSource"
LabelMenuConfiguration="1"
Filter=""
runat="server"/>
<PublishingWebControls:VariationsLabelEcbMenu
ID="variationLabelMenu"
DataSourceID="LabelMenuDataSource"
DisplayText=""
IsCallbackMode="true"
runat="server"
/>
<PublishingWebControls:VariationDataSource
ID="VariationDataSource1"
LabelMenuConfiguration="1"
Filter=""
runat="server"
/>
</div>
After that you can have your lang dropdown like below :-