Dear Huynh Trong Khanh,
One of the transliteration systems (there are many) which is commonly in use, is the IAST (International Alphabet of Sanskrit Transliteration). According to the English Wikipedia entry, this standard was agreed on in Geneva in 1894 on the International Congress of Orientalists.
I don't know what modifications of earlier systems go back to Rhys Davids, but according to another source, an earlier system by Halhed was documented in 1776 already, and other scholars like Monier-Williams and Max Müller used systems that look like modifications or adaptations of earlier systems. You can find a table comparing several systems if you follow this link:
Summary: I wouldn't call the IAST system the "invention" of any particular person, but only a convention and adaptation/modification, or attempt of standardisation of already existing systems. The first "Romanization system" might possibly stem from the Dutch Marcus Zuerius van Boxhorn (1612-1653) who was the first one to discover similarities between Indo-European languages. Later in the 18th century, Sir William Jones, Henry Thomas Colebrook, and the earlier mentioned Nathaniel Halhed did further research on this topic and wrote Indic words with Roman script.
Regarding dictionaries as a tool for translation: There are many kinds of dictionaries, from more primitive ones in the form of word lists to very detailed ones, giving several contexts in which a word may occur and several meanings such a word could take (and providing more or less information about etymology, parallels in other languages etc.). There is indeed no simple word-to-word corresponce from one language to another (otherwise we would get perfect translations by machine translating), this holds true for any language pair. In lexicography, the bigger the corpus of texts under examination, the more details about the occurence of a word an its (possible) meaning you can get.
The PTS dictionary was a collaborative, 40-year efffort of several scholars. I don't know in how far they used bilingual Pali-Sinhala tools (and I don't know whether there were bilingual Pali-Sinhala dictionaries at that time), but they certainly did not just look for equivalent words from Sinhala to English when compiling their dictionary.
I hope this was of some use.
Kind regards,
Susanne
PS: For more detailed (but more general) information about Rhys Davids, you can find some reading here:
Gesendet: Montag, 09. Februar 2015 um 14:51 Uhr
Von: "KHANH TRONG HUYNH testsuda@... [palistudy]" <palistudy@yahoogroups.com>
An: "palistudy@yahoogroups.com" <palistudy@yahoogroups.com>
Betreff: [palistudy] Some question about Pāḷi word system
Dear all,
I have 2 questions as below:
1. The Latin letters system for Pāḷi was exactly an invention of T.W Rhys Davids or not, if not, could you please suggest me its origin
2. For Pāḷi as well as language in general, how people make a dictionary for it. I mean, for example. How the Western scholars define the meaning of a Pāḷi word as an equal English word, they just merely translate from Sinhalese - cause I know that Sri Lanka was a British colony, or they use another more comprehensive & systematic method? In case that there's no fixed word-meaning system of Pāḷi, how can we define a meaning of a Pāḷi word in a particular context of a text?
In our Vietnam country, as I know, the Vietnamese meaning of Pāḷi words is just translated from English
Hope to receive your responses
Sincerely yours,
Huynh Trong Khanh