ISO 15919 is an international standard on the romanization of many Indic scripts, which was agreed upon in 2001 by a network of the national standards institutes of 157 countries. However, the Hunterian transliteration system is the "national system of romanization in India" and a United Nations expert group noted about ISO 15919 that "there is no evidence of the use of the system either in India or in international cartographic products."
Another standard, United Nations Romanization Systems for Geographical Names (UNRSGN), was developed by the United Nations Group of Experts on Geographical Names (UNGEGN) and covers many Indic scripts.
ALA-LC was approved by the Library of Congress and the American Library Association and is a US standard. IAST is not a standard (as no specification exists for it) but a convention developed in Europe for the transliteration of Sanskrit rather than the transcription of Indic scripts.
As a notable difference, both international standards, ISO 15919 and UNRSGN transliterate anusvara as ṁ, while ALA-LC and IAST use ṃ for it. However, ISO 15919 provides guidance towards disambiguating between various anusvara situations (such as labial versus dental nasalizations), which is described in the table below.
Only certain fonts can support all Indic ISO 15919 Unicode character sets. For example, Tahoma supports most Unicode characters needed for Indic language transliteration. Arial and Times New Roman font packages that come with Microsoft Office 2007 (but not with MS Office 2003 or earlier) also support most "Latin extended additional" ISO 15919 Unicode characters like ḑ, ḥ, ḷ, ḻ, ṁ, ṅ, ṇ, ṛ, ṣ, ṭ, etc.
The table below shows the differences between ISO 15919, UNRSGN and IAST for Devanagari transliteration.
ए / े
To distinguish between long and short 'e' in Dravidian languages, 'e' now represents ऎ / ॆ (short). Note that the use of ē is considered optional in ISO 15919, and using e for ए (long) is acceptable for languages that do not distinguish long and short e.
ओ / ो
To distinguish between long and short 'o' in Dravidian languages, 'o' now represents ऒ / ॊ (short). Note that the use of ō is considered optional in ISO 15919, and using o for ओ (long) is acceptable for languages that do not distinguish long and short o.
ऋ / ृ
In ISO 15919, ṛ is used to represent ड़.
ॠ / ॄ
For consistency with r̥
ऌ / ॢ
In ISO 15919, ḷ is used to represent ळ.
ॡ / ॣ
For consistency with l̥
ISO 15919 has two options about anusvāra. (1) In the simplified nasalization option, an anusvāra is always transliterated as ṁ. (2) In the strict nasalization option, anusvāra before a class consonant is transliterated as the class nasal—ṅ before k, kh, g, gh, ṅ; ñ before c, ch, j, jh, ñ; ṇ before ṭ, ṭh, ḍ, ḍh, ṇ; n before t, th, d, dh, n; m before p, ph, b, bh, m. ṃ is sometimes used to specifically represent Gurmukhi Tippi ੰ.
ṅ ñ ṇ n m
Vowel nasalization is transliterated as a tilde above the transliterated vowel (over the second vowel in the case of a digraph such as aĩ, aũ), except in Sanskrit.