Bethesda cites Old English recordings of Beowulf as one of the chief inspirations for how the dragon language would sound. However, the connection goes much deeper than that.

I'm currently reading through Beginning Old English, and I've come across some interesting passages that apply as much to Dovahzul as they do to Old English. I thought I'd share some excerpts that I think help reveal Bethesda's original vision for the language.

The Alphabet

It is a considerable task to create a written form of a language that for 400 years had mainly been spoken. The scribes who occasionally glosed difficult Latin words in Old English had used a mixture of the roman alphabet used for Latin, and the ancient runic alphabet used by Germanic tribes on the continent. Runes were straight-sided characters, suitable for carving on hard surfaces, such as wood, bone, or stone.

p. 8

Like Old English, Dovahzul features straight-sided characters meant for carving, only in this case by a dragon's claw. It's interesting to think about how long Dovahzul existed as a spoken language only, or if a writing system was inherent to the language.

Similarly, the use of modern punctuation imposes a choice between capitals and lower-case ... which in turn imposes an interpretation  of personal name or vocabulary word. ... Notice particularly the almost total lack of manuscript punctuation. The use of commas, exclamation marks, full stops, question marks and so on in printed editions of Old English poetry is modern, and varies from edition to edition.

p. 105-106

This passage is discussing personal names (which we'll get to later), and how it's difficult to recognize them because the manuscripts do not feature capitalization. Lack of punctuation is something that Old English and Dovahzul also share, and for Dovahzul I think it's something very valuable to its tone that would be lost with the use of invented punctuation.

Below are some images of Old English manuscript and Dovahzul writing.

Personal Names

Old English personal names were made up vocabulary words, often in compounds that do not make literal sense. The main characters in one of the texts ... are called Cynewulf and Cyneheard, names that translate as 'royal-wolf' and 'royal-hard'. The hero of the epic poem Beowulf has a name that literally means 'bee-wolf', but figuratively perhaps means 'bear' (bee = honey, wolf = fierce animal; fierce animal that steals honey = bear). This is an aspect of Old English on which J. R. R. Tolkien drew extensively when naming characters in The Lord of the Rings. For instance, the name of the villain, Saruman ..., is taken from OE searu 'trickery' plus 'man', to give a compound with the sense of 'man of trickery'.

p. 31

Bethesda followed suit by naming their dragons with vocabulary words, in compounds that don't make literal sense (Odahviing = "snow hunter wing," or more conventionally, "winged snow hunter"), but convey the aspects and elements important to that dragon's character. This ended up becoming both neat lore and an awesome gameplay mechanic, in which a dragon's name is also a Shout.

The Dragon Priests also borrow names from vocabulary.

Compound Words

Anglo-Saxon poets often use roundabout expressions, known as 'circumlocution' or 'euphemism', in preference to more straightforward terminology. For instance, God is referred to here as heofan-rÄ«ces Weard 'Guardian of the heavnly kingdom' and man-cynnes Weard 'guardian of mankind', while people are described as eorþan bearnum 'the children of the earth'.

Compounding is particularly common in Old English poetry. It tends to increase the weight of meaning, since a compound can express an idea more concisely than a descriptive phrase.

...

Some compounds are metaphorical rather than literal, and are known as 'kennings'. The meaning of middan-geard ('middle-dwelling'; the source of Tolkien's 'Middle-Earth' ... ) derives from the medieval belief that earth was mid-way between Heaven and Hell.

p. 100

Dovahzul clearly takes inspiration here with compounds like suleyksejun "dominion" (lit. "power-of-king") and vennesetiid "the currents of time" (lit. "winds of time"). We also see euphemism is a number of Word Walls, for example this one which references Hermaeus Mora:

Pah werid morokei Miraak
zok suleykaar do pah
sonaak wen mul bolaav
naal fahluaan do jul

All praise the glorious Miraak,
most powerful of all
priests, whose strength was granted
by the gardener of mankind.

"Gardener of mankind" here refers to Hermaeus Mora, rather than naming the Daedric Prince directly.

Poetic Style & Vocabulary

The main stresses are usually long syllables ... and tend to be important words like nouns or adjectives. There are in any case fewer grammatical words than in prose. Old English poetry is a very concentrated style of writing, and the omission of many of the grammatical words, which carry less meaning, packs each line full of significant terms.

p. 98

This concept is applied very directly to the Word Walls, as can be seen in the example below:

Qethsegol vahrukiv kril
Thjodrek wo dir zohungaar
ko grah do vith okaaz

(This) stone commemorates (the) brave
Thjodrek, who died heroically
in (the) Battle of (the) Serpent Sea.

One question that comes up often is that of synonyms; krein vs. shul, sivaas vs. sunvaar, or fod vs. rul. The answer may lie in Old English:

Partly because of the demands of alliteration, Old English poetry needed a wide vocabulary, with a range of synonyms for recurring themes such as man, warfare, and God. For instance, Metod and Scieppend both mean 'Creator', and Dryhten and FrÄ“a both mean 'Lord'. The vocabulary of Old English poetry is to some extent different from the vocabulary of prose, and here the words Metod 'God', firas 'men', and FrÄ“a 'Lord' are recorded only in poetry. Later stages of the language also have a poetic register - a sense that certain words are primarily suitable for use in poetry - but this is particularly pronounced in Old English, where a sizeable proportion of the known vocabulary is restricted to the poetic corpus, and referred to as 'poetic diction'.

p. 100-101

From what little we've seen of poetry in the dragon language, we know that alliteration is perhaps not a driving factor, but rhyming could exert the same pressure to have a wealth of synonyms. What Dovahzul also has that Old English does not is a set of words that would be used primarily for Shouting. This results in words like ah "hunter" and nir "to hunt."

Since the volume of dragon language poetry we have available is very small, it is difficult to say what Dovahzul's poetic diction might look like.

Verb Tense

​We also need to be aware that Old English writers do not always use these verbal combinations in exactly the way that we would today. That is, sometimes Old English writers use simple present-tense forms when we would expect a combination of words that expresses duration ... . So long as we are famliar with the basic forms and are sensitive to the possibility of variation, we should become confident in our interpretations of older texts.

p. 84

One of Dovahzul's signature traits is its relatively few verb tenses, in particular its lack of distinction between present and past tense. Bethesda takes the above notion to the extreme, and relies heavily on context to determine tense.

In the Word Wall described above, we know that vahrukiv is probably present tense because the qethsegol is still standing. We then know that dir is past tense, because the subject, Thjodrek, is already dead.

Negatives

The negative is often formed ... by putting ne before the verb. There is also another word, nā, which can be translated as 'not'.

...

Some common verbs, as you will have noticed, combine with ne to form a single negative word: nis (ne + is 'isn't'), nylle (ne + wille 'don't wish'), and nyste (ne + wiste 'don't know'). This kind of combination also occurs with the pronoun nān (ne + Än 'none').

Ni is the Dovahzul negative, along with perhaps neh "never." It is used in the exact manner described above; nust ni hon "they didn't listen," or ni faas, dovahkiin "I don't fear you, Dragonborn."

The obvious inspiration from the second paragraph is nis "cannot." Perhaps this implies the word for "can" is something that combines more readily with ni than our current word vis. Maybe his. There could be other, new words that stem from this, such as naaz "without mercy / not having mercy," or naam "not serve / never serve"; zu'u fen naam "I will never serve you."

Differences

Old English is much different from modern English. It is grammatically and phonetically closer to German, with the four grammatical cases and more flexible word order in its syntax. Nouns decline in a way that help communicate the subject and object of a sentence. As a German example; Den Junge liebt der Hund "The dog loves the boy." The way this sentence is ordered, it literally reads "The boy loves the dog." In German, the article den makes it clear that "the boy" is the object of the sentence rather than "the dog."

In a language like Dovahzul, where there declension and conjugation are limited to extremes, word order becomes very important. It makes sense that Bethesda chose to stick with English's syntax, not only because it's familiar and makes the language easier to learn, but because both English and Dovahzul lack the grammatical intricacies that languages with more flexible syntax possess.

Summary

Bethesda did their homework and made a language that successfully embodies its speakers and draws from real-world inspiration in ways that make sense. We can use these reference points to inspire our own work in the language and consider Bethesda's original vision.

This clears up so much! Thank you!