For a small collection that you'd like high recall for, you might use 4 streams that differ only in their stemmers: none (boost for exact match), case (boost for exact characters), delanguage (boost for only being pluralized/accented differently), english (get better recall by pulling in other words).
To set a global stream configuration, use the graphical interface on the Configuration > Indexing pane.
To set an entire document to use a different stream definition than the global, add the stream definition at the document level:
<document> <vse-index-stream segmenter="japanese" kb="japanese-indexing" stem="depluralize"/> ...content in Japanese... </document>
To set a content to use a different stream definition than the document or global level configuration, add the stream definition at the content level:
<content name="full-name"> <vse-index-stream segmenter="literal" /> Joe Developer </content>