You can use Rest API to get data category group labels. Try GET request to below URI as:
/services/data/v43.0/support/dataCategoryGroups/<Your DataCategoryGruop Name>/dataCategories/All?sObjectName=KnowledgeArticleVersion
You will be getting details including name, label and its child category details. Parse the JSON response and do your logic.
Sample response looks like:
{
"childCategories" : [ {
"childCategories" : null,
"label" : "Demo 1",
"name" : "Demo_1",
"url" : "/services/data/v43.0/support/dataCategoryGroups/Test/dataCategories/Demo_1?sObjectName=KnowledgeArticleVersion"
}, {
"childCategories" : null,
"label" : "Test1",
"name" : "Test1",
"url" : "/services/data/v43.0/support/dataCategoryGroups/Test/dataCategories/Test1?sObjectName=KnowledgeArticleVersion"
}, {
"childCategories" : null,
"label" : "Test2",
"name" : "Test2",
"url" : "/services/data/v43.0/support/dataCategoryGroups/Test/dataCategories/Test2?sObjectName=KnowledgeArticleVersion"
} ],
"label" : "All",
"name" : "All",
"url" : "/services/data/v43.0/support/dataCategoryGroups/Test/dataCategories/All?sObjectName=KnowledgeArticleVersion"
}