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I'm planning to go on a picnic tomorrow.
Literal
Tomorrow [topic-は] picnic [purpose-に] go intend-is.
An alternate phrasing of 'I plan to go on a picnic tomorrow,' this time with は on 明日. The は frames tomorrow as the topic — 'as for tomorrow, I plan to go on a picnic' — a subtle background-setting nuance compared with a bare 明日 + verb.