The stitch tongue is a projection on the presser foot which helps form the stitch. See the picture at "Stitch Tongue for 118-99861" reference to see the projection that I'm talking about. The actual hole would be the stitch throat. Some sewing machine presser feet have stitch tongues as well. The only bilingual reference I found gives butée-guide, which works because the stitch is forming around the projection. However, it is the only site to use that term. Personally, I think of languette for tongue in this context, and I did find it used. However, there aren't many examples of it in use either.

Stitch Tongue for 118-99861 [see picture to see the projection that is the stitch tongue]
( Model Number : MO-2300, 117-92900 )
http://jake200708.en.ec21.com/Stitch_Tongue_for_118_99861--2...

Sur le nouveau système automatique ARRÊT de CHAÎNETTE ABT-17, le fil de chaînette est maintenu et placé sous la languette du pied presseur en fin de cycle de couture, il est ainsi possible de réaliser des points plus serrés au début de la
couture suivante.
www.yamato.de/leaflet/pdf/pdf/abt17.pdf

Un seul réglage de la quantité de fil, la languette du point se déplace en même temps que le couteau
http://comptoir-phoceen.fr/mac/contents/fr/d35.html

A “good-to-buy” economy type overlock machine for sewing outer knitwear. Various user friendly features are available as the basic design of the machine is based on Yamato’s Japan made cutting edge overlock machine. Besides, you can widen the overlock width up to 8mm by simply changing presser foot stitch tongue and stitch plate without any adjustment.

Les divers dispositifs faciles à utiliser, sont disponibles en standard grâce à la conception de la machine faite sur la base de la machine Yamato fabriquée au Japon.
Vous pouvez aussi augmenter la largeur du surjet fini jusqu'à 8mm en changeant simplement la butée-guide du pied presseur et la plaque à aiguilles, sans aucun réglage.
http://www.yamato.de/IMB2003/IMB_Photos/26_CZ6020/26.html



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Note added at 9 hrs (2009-06-01 17:49:04 GMT)
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Alternate translation: doigt mailleur

I kept thinking that there had to be a better term for this phrase, one which was more in use, so I kept looking. An alternate name for the stitch tongue is stitch finger (or chaining finger). As previously stated, the stitches are formed around the projection. And I should point out that, in addition to presser feet, needle plates can have also have stitch fingers (or tongues).

[this site has a lot of pictures so check it out :-)]
Merrow EXC-546 Presser Foot Finger
Merrow 6-193-D Needle Plate Chaining Finger
http://store.merrow.com/category/10239020681/1/Finger.htm

17. Stitch finger lever (SL1T-X)

17. Languette d’escamotage du doigt mailleur
(SL1T-X)
www.aisin.at/data/datei413c1f9fa17ac.pdf

IMPORTANT:
Never turn the cutting width dial if threads are forming a stitch around the chaining finger. Remove threads by raising presser foot and gently pulling them to the back.
IMPORTANT:
Ne jamais tourner la molette de largeur de coupe si les fils forment un point autour du doigt mailleur. Retirer les fils en relevant le pied presseur et en les tyrant doucement vers l’arrière
http://www.janome.com/documents/File/ManualFile/Instbook1100...

Huskylock 905
Caractéristiques & Avantages
• 2, 3, 4 fils …
• Guides pour fil décoratif
• Réglage du doigt mailleur …
http://www.husqvarnaviking.com/fr/880_814.htm

Réglage de la machine : Point talon plat à 2 fils,longeur N-3,largeur 6, doigt mailleur N.
http://www.stecker.be/shop/contents/fr/p2470.html


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Note added at 9 days (2009-06-10 21:28:02 GMT) Post-grading
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You're welcome, Marianne, and thank you! :-)