Cytoplasm is the semitransparent fluid that suspends other organelles.

This stained glass is semi-transparent.

Yes, semitransparent and diaphanous are similar in meaning as they both refer to something that allows light to pass through but is not completely transparent. They can be used interchangeably in certain contexts.

Translucent or semitransparent materials like fiberglass or stained glass only let in some light.

you need to wipe the excess stain off the deck with a clean rag. It will never dry and it will float to the top of the sealer