Steps to reproduce:

Looks like another issue similar to #7740
The Hindi characters रु and चि, when they are presented as a word together silences NVDA.

1. Open a document.
2. Paste the symbols रु and चि in the document without a space between them.
3. Read the current line with ESpeak.

WARNING: DO NOT READ THIS NEXT LINE WITH ESPEAK WITHOUT WARNING!!!!!!!!
Note: the word is रुचि

Expected behavior:

NVDA should read the line as expected.

Actual behavior:

NVDA is silent and requires a restart to resume properly. The log is reporting that it is still reading the text.

System configuration:

NVDA version: master-14674,47a0147d
NVDA Installed or portable: Installed
Windows version: Windows 10,1703, and Windows 8.1
Name and version of other software in use when reproducing the issue: Microsoft Word, Notepad

Other questions:

Does the issue still occur after restarting your PC? Yes
Have you tried any other versions of NVDA? NVDA 2017.4RC3 and earlier

I will try to do a bisect tomorrow to see if I can track down the commit that is causing this issue, but it very likely could be the same issue found in #7740.