Note: Sorry if this post is needlessly detailed, I understand a lot of these details don't affect the question much. I thought I'd bring them up anyways since this is quite the unique situation for the development of a shared language. You get the gist of it.
In this world, there is a verdant land called Apylecus and in tribal times (similar to the late late Neolithic age on Earth), two different nomadic tribes migrate there and eventually become sedentary. The land is extremely lush, one of the most habitable lands in the entire world and is protected by a vast mountain range that encircles the region. Geographically, the land is like a dense taiga forest. Food is so abundant, the two tribes are able to become sedentary even though they rely on a hunter gatherer system and subsistence economies.
The two tribes live here in their small, scattered villages. Each tribe has multiple settlements united by a single government. Literally for hundreds of years they live in the same region, the population slowly increasing over time. Eventually they develop basic agriculture and near the end of the period the agriculture becomes sufficiently advanced and they experience a population boom.
After 1500 years the tribes finally merge after a large final war and go on to create a civilization, but that isn't the focus of this question. What I want to know is will their languages realistically merge with each other before this happens and how long would that take?
The two tribes are the Apylessi and Nageqim tribes.
They are the same race but hail from very distinct regions during their nomadic years. This is one of their few similarities.
The Apylessi and Nageqim live close to each other for a long time (roughly 1500 years) and fight many countless wars, always resulting in stalemates or ceasefires. Their technology progress at the same rate, when one tribe makes an innovation or discovery it isn't long before the other tribe steals it. A famous example of this was when the Nageqim stole domesticated sheep from the Apylessi who had managed to domesticate the animal first.
Over time, how feasible is it that these two languages would merge with each other and how long would it probably take?
Things to keep in mind:
The Apylessi and Nageqim migrated from different regions in the world and speak two completely distinct languages. These languages have no similarities.
The Apylessi and Nageqim are the same race, but have genetic differences.
They never migrate out of the region because it is extremely lush with abundant sustenance.
It is not uncommon for an Apylessi or Nageqim walking alone through the forest to encounter a man or woman from the other tribe. Meetings and encounters are frequent. In times of war, they would usually immediately attack each other. In times of peace, they would usually be very cautious.
The Apylessi and Nageqim are fairly primitive, with societies similar to the Late Neolithic Period with civilization right around the corner. Agriculture becomes prevalent halfway through the 1500 year time span and really becomes developed near the end which results in an advancement of technology.
- They have no systems of writing.
For hundreds of years, the Apylessi and Nageqim settlements are always never more than a seven days walk apart from each other at the very most. With an average distance of three days and some settlements even within a few hours distance of each other.
These close settlements are surprisingly common, though not the most common type of settlement. Interestingly the two tribes sometimes "communicate" with each other here from the onset. Initially, they are hostile and continue to be hostile during most of history and naturally these settlements suffer the most during wars since they edge towards territorial borders. Interestingly, in the late years of the 1500 year era when agriculture begins to become developed, these settlements begin trading with each other. Think, wool and other items. This results in mixed views from the isolated settlements, ranging from outrage to paranoid acceptance. Ties between the two tribes become the most friendly here of any region, though there are no alliances of any kind.
The Apylessi and Nageqim never traded with each other in any other circumstances other than the late sproadic trading practiced in close settlements, since they hated one another. Individuals would sometimes meet each other in the forest and trade, though this was infrequent and frankly quite rare.
Settlements within each tribe did trade with other settlements in the tribe.
The most densely populated areas for the Apylessi are usually midways away from the territorial borders, while the Nageqim have sizeable villages near the territorial borders. I doubt this matters much.
A third splinter tribe is never formed.
The Apylessi and Nageqim frequently fight many wars, but there is never a victor. No significant settlement is ever conquered. Territory is gained and lost in an endless struggle, going back and forth. All the while, neither tribe ever retreats and they remain in the same region and always at equal strength. There are periods of peace and periods of war.
The Apylessi and Nageqim never ally with each other. To suggest such a thing would be ridiculous.
The Nageqim practice slavery, while the Apylessi do not. Slaves rarely escape. Slavery is a large part of the Nageqim society and Apylessi slaves are in decent number but only form roughly a quarter of their total slave population
On average, their populations remain equal to each other. Slowly growing as agriculture becomes more dominant in their societies. Shortly after arriving in Apylecus as nomadic tribes, the total population is roughly 649 people, split equally between the two tribes. During 1500 years the population steadily increases as agriculture becomes more developed. The population at the end of the 1500 years is roughly 7000, once again split equally between both tribes.
The Apylessi and Nageqim literally despise each other and many of their myths and legends antagonise the other.
If you have any questions I will answer them. Honestly I'm unsure if their languages would ever merge at all, though 1500 years is a very very very long time to spend in close proximity to another tribe. This is why I wonder.