Polylang is a fantastic plugin that adds multilingual support to WordPress:

Polylang allows you to create a bilingual or multilingual WordPress site. You write posts, pages and create categories and post tags as usual, and then define the language for each of them. The translation is optional. The plugin does not integrate automatic or professional translation.

After installing and activating this Extension, SearchWP will limit search results to the active language of your Polylang-powered content segmentation.