They were all writing some keys to HKLM\SOFTWARE\Microsoft\Speech\PhoneConverters\Tokens\Universal
As for some XP systems the settings here aren't correct, and what happens is that voices which doesn't have language ID set to 409 doesn't work.
Who would have thought that PhoneConverters registry settings would affect TTS on Windows?
Basically here's the keys you need to add to your installer: (Wix example)
<registrykey action="create" id="REGMSUniversalPhoneConvFix" key="SOFTWARE\Microsoft\Speech\PhoneConverters\Tokens\Universal" root="HKLM">
<registryvalue type="string" value="Universal Phone Converter">
<registryvalue name="CLSID" type="string" value="{9185F743-1143-4C28-86B5-BFF14F20E5C8}">
<registryvalue name="PhoneMap" type="string" value="I 0069 Y 0079 IX 0268 YX 0289 UU 026F U 0075 IH 026A YH 028F UH 028A E 0065 EU 00F8 EX 0258 OX 0275 OU 0264 O 006F AX 0259 EH 025B OE 0153 ER 025C UR 025E AH 028C AO 0254 AE 00E6 AEX 0250 A 0061 AOE 0276 AA 0251 Q 0252 EI 006503610069 AU 00610361028A OI 025403610069 AI 006103610069 IYX 006903610259 UYX 007903610259 EHX 025B03610259 UWX 007503610259 OWX 006F03610259 AOX 025403610259 EN 00650303 AN 00610303 ON 006F0303 OEN 01530303 P 0070 B 0062 M 006D BB 0299 PH 0278 BH 03B2 MF 0271 F 0066 V 0076 VA 028B TH 03B8 DH 00F0 T 0074 D 0064 N 006E RR 0072 DX 027E S 0073 Z 007A LSH 026C LH 026E RA 0279 L 006C SH 0283 ZH 0292 TR 0288 DR 0256 NR 0273 DXR 027D SR 0282 ZR 0290 R 027B LR 026D CT 0063 JD 025F NJ 0272 C 00E7 CJ 029D J 006A LJ 028E W 0077 K 006B G 0067 NG 014B X 0078 GH 0263 GA 0270 GL 029F QT 0071 QD 0262 QN 0274 QQ 0280 QH 03C7 RH 0281 HH 0127 HG 0295 GT 0294 H 0068 WJ 0265 PF 007003610066 TS 007403610073 CH 007403610283 JH 006403610292 JJ 006A0361006A DZ 00640361007A CC 007403610255 JC 006403610291 TSR 007403610282 WH 028D ESH 029C EZH 02A2 ET 02A1 SC 0255 ZC 0291 LT 027A SHX 0267 HZ 0266 PCK 0298 TCK 01C0 NCK 0021 CCK 01C2 LCK 01C1 BIM 0253 DIM 0257 QIM 029B GIM 0260 JIM 0284 S1 02C8 S2 02CC . 002E _| 007C _|| 2016 lng 02D0 hlg 02D1 xsh 02D8 _^ 203F _! 0001 _& 0002 _, 0003 _s 0004 _. 2198 _? 2197 T5 030B T4 0301 T3 0304 T2 0300 T1 030F T- 2193 T+ 2191 vls 030A vcd 032C bvd 0324 cvd 0330 asp 02B0 mrd 0339 lrd 031C adv 031F ret 0331 cen 0308 mcn 033D syl 0329 nsy 032F rho 02DE lla 033C lab 02B7 pal 02B2 vel 02E0 phr 02E4 vph 0334 rai 031D low 031E atr 0318 rtr 0319 den 032A api 033A lam 033B nas 0303 nsr 207F lar 02E1 nar 031A ejc 02BC + 0361 bva 02B1 G2 0261 rte 0320 vsl 0325 LG 026B NCK3 0297 NCK2 01C3 LCK2 0296 TCK2 0287 JC2 02A5 CC2 02A8 DZ2 02A3 TS2 02A6 JH2 02A4 CH2 02A7 SHC 0286 rhz 02B4 QOM 02A0 xst 0306 T= 2192 ERR 025D AXR 025A ZHJ 0293">
<registrykey action="createAndRemoveOnUninstall" id="REGMSUniversalPhoneConvFixAttr" key="Attributes">
<registryvalue name="Language" type="string" value="436;41c;401;801;c01;1001;1401;1801;1c01;2001;2401;2801;2c01;3001;3401;3801;3c01;4001;42b;42c;82c;42d;423;402;455;403;c04;1004;1404;41a;405;406;465;413;813;809;c09;1009;1409;1809;1c09;2009;2409;2809;2c09;3009;3409;425;438;429;40b;80c;c0c;100c;140c;180c;456;437;807;c07;1007;1407;408;447;40d;439;40e;40f;421;410;810;44b;457;412;812;440;426;427;827;42f;43e;83e;44e;450;414;814;415;416;816;446;418;419;44f;c1a;81a;41b;424;80a;c0a;100a;140a;180a;1c0a;200a;240a;280a;2c0a;300a;340a;380a;3c0a;400a;440a;480a;4c0a;500a;430;441;41d;81d;45a;449;444;44a;41e;41f;422;420;820;443;843;42a;">
</registryvalue>
</registrykey>
</registryvalue>
</registryvalue>
</registryvalue>
</registrykey>
It tells the SAPI tts what languages should be "accepted". The problem is that these keys might be correct on some computers, or even modified for other purposes, and then again rendering a voice non-functioning. (If you have old Voxit Budgie Pro versions with certain voices, you will experience this issue, as some of the installers write other settings to this area).
If you are developing SAPI voices and are experiencing this issue, please look at the Language code under the Attributes setting for your voice in the registry.
The path for your voice should be: (replace YourVoice with the proper name)
