I’ve created a British keyboard layout for Mac OSX that features romanised Pali diacritics.
All of the characters are accessible by using the left Alt (aka option or ⌥) key plus a special key (tilde ~, full stop ., minus -) which represent the diacritic to apply. This changes the keyboard state so that if the next normal upper or lower case character pressed is one of the romanised Pali characters that uses diacritics, then the diacritic is applied to that character.
Press left Alt + minus, followed by a,A, i,I, u,U to get macron:
Press left Alt + tilde, followed by n,N to get tilde:
Press left Alt + full stop, followed by t,T, d,D, n,N, l,L, m,M to get dot-below:
Press left Alt + shift + full stop (less than symbol <), followed by n,N to get dot-above:
In the case of the dotted characters, you can remember the normal dot as being dot-below, and shift-dot as being dot-above, similar to how lower case characters which don't use the shift key are normally lower in height, and upper case characters which use the shift key normally occupy the upper, or higher part of the line.
It can be a bit tricky at first to get the dot-above with upper case characters.
e.g., to produce Ṅ you need to press left Alt + shift + full stop, then shift + n.
Save the keyboard layout in ~/Library/Keyboard Layouts/
[EDIT: 2014-04-26] As pointed out by Christoph, some web browsers (such as Safari) might save the file as “British with Pali.keylayout.txt“. You must rename it to remove the “.txt”, so that it’s just “British with Pali.keylayout”.
Log out then log back in again.
Open System Preferences -> Language and Text -> Input Sources
Tick “British with Pali”
Tick “Show Input menu in menu bar”
Click on the Input menu bar and select “British with Pali”
From now on you will be able to enter the Pali diacritics.
Your keyboard layout will stay like this from now on.
If you don’t need to change the layout again, feel free to go back to the Input Sources panel of System Preferences and untick “Show Input menu in menu bar”.