You can filter search by using a filters
array in your JSON, as shown here.
For example:
{
"query": "OSH",
"start": 0,
"rows": 10,
"lang": "ENGLISH",
"filters": [
{
"type": "QueryFilter",
"negative": false,
"query": "lang:en"
}
]
}
You will find more information on this page.