Paraphrase:

the juristic act which creates the trust—the act of executing the trust deed or otherwise transferring the trust property to the trustees—may be governed by a law different from that which governs the interpretation, administration and other aspects of the trust.

The legal action that establishes the trust, such as signing the trust deed or transferring property to the trustees, may be subject to a different law than the one governing the interpretation and administration of the trust.