The next stage in the decipherment of Old Persian cuneiform during the 1820s–1830s built directly on Georg Friedrich Grotefend's foundational work from the early 1800s. This period saw incremental advances through linguistic comparisons (especially to Sanskrit and Avestan), identification of additional signs, grammatical insights, and better readings of royal titles and place names.

• Rasmus Christian Rask (Danish linguist, 1787–1832): In 1826, Rask made a key breakthrough by correctly identifying the signs for m and n. This allowed him to recognize the genitive plural ending -ānām (corresponding to Sanskrit -ānām) in phrases like "king of kings" (xšāyaθiya xšāyaθiyānām). This was a major step forward, as it provided strong evidence linking Old Persian to Sanskrit and other Indo-Iranian languages, confirming its Indo-European nature and advancing grammatical understanding beyond mere name-guessing.
• Antoine-Jean Saint-Martin (French orientalist): In 1822, Saint-Martin contributed by confirming and expanding on Grotefend's identifications. Using a quadrilingual inscription (including Egyptian, recently deciphered by Champollion), he validated readings for royal names like "Xerxes" and "king." He attempted to outline an Old Persian alphabet, correctly identifying about 10 of the 39 signs he proposed, though his overall system remained partial and built on earlier guesswork.
• Eugène Burnouf (French scholar and expert in Avestan/Sanskrit, 1801–1852): In the mid-1830s (particularly 1833–1836), Burnouf achieved major progress. Drawing on his deep knowledge of Avestan (from Zoroastrian texts like the Yasna) and Sanskrit cognates, he identified additional consonants such as k and z. Crucially, he recognized that one of the Persepolis inscriptions contained a list of satrapies (provinces) from Darius's empire, using geographic names to assign phonetic values and refine the alphabet. By 1836, he published a near-complete alphabet of about 30 letters, with most correctly deciphered, and translated portions of inscriptions (e.g., from Mount Elvend and Van).
• Christian Lassen (Norwegian-born German Indologist, professor at Bonn): Also in 1836, Lassen independently refined Grotefend's framework in his work Die altpersischen Keilinschriften von Persepolis. He improved grammatical analysis, addressed issues like vowel absence in some readings (making words unpronounceable if strictly followed), and contributed to fixing letter values through comparisons with Sanskrit and Avestan. His contributions overlapped with Burnouf's (they corresponded), but Lassen emphasized systematic grammar and proved Old Persian was a sister language to both Zend (Avestan) and Sanskrit, not identical to Zend. Later (1845), he collected and published known inscriptions.

These scholars collectively transformed the field from speculative name-matching into a more scientific philological effort, establishing Old Persian as an Indo-Iranian language closely related to Sanskrit. Their work set the stage for Henry Rawlinson's full decipherment of the Behistun inscription in the 1840s, which finally unlocked the trilingual texts and opened the door to Elamite and Babylonian cuneiform.This collaborative, international progress in the 1820s–1830s turned partial guesses into a reliable phonetic and grammatical foundation.