First strokes of a new Romance conlang - Germanech

Hi!

These are the first strokes of a sketch of a new Romance conlang I am
currently
working on.  It has not yet gone much beyond the basic idea (a Romance
language which might have evolved if the Romans had been successful in
conquering Germany, built on a Germanic substratum similar to the way
Brithenig is built on a Celtic substratum), but I thought you might be
interested in the matter.
The basic assumption might be historically implausible (if Germany is
conquered and firmly romanized, this might save the Empire from the
barbarian invasions, thus preventing the break-up of Latin in distinct
Romance languages), but I think the fun of it is worth trying!

Germanech is a Romance language, i. e. it evolved from Vulgar Latin
after the fall of the Roman Empire.  It is also a thought experiment:
what might have happened if Varus's campaign in Germany had not been
the disaster it was in our history, but had succeeded in gaining a new
province.  Germanech is what might be spoken in Germany today if
Vulgar Latin had replaced the Germanic dialects as vernacular
language.  In a sense, Germanech is to German what Brithenig is to
Welsh and Breathanach to Irish.

Phonology

The basic assumption is that Germanech is a Romance language with a
number of sound changes characteristic for German applied to it.
These changes are:

1. Umlaut.  The back vowels /a, o, u/ are fronted if the next syllable
   contains /i/ or /j/.  This change remains effective even where
   the segment that originally caused the umlaut got lost later.

2. Consonant shift.  The unvoiced stops are turned into homorganic
   fricatives or affricates in certain contexts:

   /p, t, k/ -> /f, s, x/    after vowels and liquids

   /p, t/    -> /pf, ts/     initially and after nasals

   Some southern dialects also shift /k/ to /kx/ analogous to the
   second rule.  Some northern dialects do not shift /p/ into /pf/.
   The northernmost dialects do not shift consonants at all.

   The phoneme /x/ is written <ch> and has two allophones:
   [x] after back vowels and [C] elsewhere.

   An /s/ resulting from shift is spelled <z>.

3. Diphthongization.  Non-low long vowels become diphthongs:

   /i:/ -> /ai/ (umlaut in the preceding syllable)
   /ü:/ -> /oy/
   /u:/ -> /au/
   /e:/ -> /ai/ (no umlaut)
   /ö:/ -> /oy/
   /o:/ -> /au/

   The diphthongs /ai/, /oy/ and /au/ are written <ei>, <äu>, <au>.

I have not yet settled on Germanech terms for these sound changes.

Spelling/Pronunciation

c       [tS] before e, i, ä, ö, ü;
        otherwise [k]
ch      [x] after a, o, u,
        otherwise [C]
cj      [tS] (causes umlaut in the preceding syllable)

g       [dZ] before e, i, ä, ö, ü;
        otherwise [g]
gj      [dZ] (causes umlaut in the preceding syllable)

h       mute (ch see above)

j       [j] (causes umlaut; cj and gj see above)

r       alveolar trilled r

s       [s]

z       [s].  The difference between <s> and <z> is that the latter
        represents an /s/ which results from consonant shift,
        while an /s/ inherited from Latin is written <s>.

The vowels are pronounced the same as in OTL German:

a, e, i, o, u have the `canonical' value, as in Spanish or Italian.
ä, ö, ü are the fronted versions of a, o, u, respectively.
ei, au, äu are pronounced [ai], [au], [oy], respectively.

Morphology

As for now, I have only very vague ideas about the morphology of the
language.
I guess that it is similar to that of most other Romance languages, but
filtered through the phonological peculiarities listed above.  Ideas are
always welcome!

...brought to you by the Weeping Elf
...latz a vau a'l Alf Lachrimantz (or something like that)