"I was explicitly instructed by my RP pronunciation teachers to avoid the
glottal stop in such cases. Let's hear the opinion of our native
English-speakers (the avoidance of [?] may well be a dialectal phenomenon)."
Piotr GASIOROWSKI, POLAND

"For my dialect (Australian), glottal stops are inserted after a
pause/beginning of an utterance(?) or before a word with particular
emphasis.* After a pure vowels (incl. air, ear; excl. he, who, hay, hoe), a
[r\] is inserted before a vowel. After a diphthong, a homorganic glide is
inserted before a vowel. A consonant before a vowel might be ambisyllabic."
Tristan McLEAY, AUSTRALIA

The glottal stop doesn't exist in French.
I was taught to produce the glottal stop in London by a native English
teacher at the onset of syllables like <ear> etc. execpt when a liaoson was
possible.

Later I found a book written by another native English teacher stating that
this was characteristic of German learners of English!

I think the best would be to consider that there is a light glottal stop and
a heavy glottal stop.

The light glottal stop whenever a liaison is feasible. It is found at the
syllabic initial of
Eng. <ear> > <an ear>
Tagalog [?a: nim] <ánim> "six" > [la 'biN '?a: nim] <labíng ánim> > [la bi
'Na: nim] <labingánim> "sixteen"
and the word initial of
Arabic [?ism] "name" > [ma: smu ka] > [ma: sm@ k] "What's your name?"

The heavy glottal stop does not exist in English. It exists in Arabic and
Tagalog.
In Arabic it is solid in the initial and final position.
[?ahl] "tribe, people"
[sama:?] "sky"
The medial ones disappear in spoken Arabics, and this elision entails the
lengthening of the vowel.
classical Arabic [bi?r] > modern Arabic [bi:r] "(water) well"

In Tagalog the heavy glottal stop only occurs in the word final position.
[baN 'ka?] <bangkâ> "canoe"
It is generally elided within a group, and a compensatory lengthening of the
vowel takes place.
<Hindî pô iyán.> [hin di: pu: 'ján] "That's not it."

I think Siamese is like Tagalog: it has the light glottal stop in the
initial syllabic position, and the heavy glottal stop in the word final
position.
[?ok (low t.)] "chest"
[lE? (high t.)] "and"

I read somewhere that Arab grammarians did make this distinction between the
light / elidable glottal stop and the heavy / un-alidable one.

Jean-Paul G. POTET, FRANCE