There is now Lidepla's reference grammar in Wikibooks:

Lingwa de planeta/Reference grammar - Wikibooks, open books for an open world
Lingwa de planeta/Reference grammar - Wikibooks, open books for an open world
Contents 1 The alphabet and pronounciation 1.1 Vowels 1.2 Consonants 1.3 Word stress 2 Simple sentence 3 Compound Sentence 4 Word 4.1 1. Noun 4.1.1 2. Pronouns that function like nouns 4.2 3.
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and Lidepla's textbook for Russian speakers:
Лингва де планета — Викиучебник

The textbook in English is under construction.

Dmitry