The changes you see on Turkey AIP charts are likely an anticipation of future reference changes, both in bearings and altimetry. To prevent confusion, the current references are explicitly mentioned.
Instruments of the past: Barometer and compass
As you know the current convention for aviation, except for ADS-B is to use magnetic direction and MSL barometric altitude. There is an exception only for polar areas, where the magnetic declination is not reliable enough, and where true directions are used.
However these two references create problems. They were very useful prior to GNSS generalized deployment, but are now two burdens.
Magnetic directions are the legal reference as of today, and must be used to interact with crews and ATCOs. However, modern navigation computers internally store and manipulate true directions, this is a simple mathematical model to make calculations for navigation.
The legal magnetic value, when needed to interact with the crew, is just derived from the stored true direction, based on a magnetic model for Earth. As I already explained in another answer, the conversion is not done homogeneously by all units, different values can coexist in the system, creating a risk.
Likewise the legal reference for altimetry is still the pressure-altitude determined by measuring the static pressure and converting it with the law in the ISA model.
It's well known this measure is not accurate at all, except in the vicinity of a weather station delivering the local pressure, hence the need to use two methods: QNE flight levels in cruise, and QNH altitudes close to the ground.
Modern navigation equipment use the geometric altitude above MSL, derived from the ellipsoidal height (HAE), which is what a GNSS receiver determines, and a model of the mean sea level above the ellipsoid (geoid).
Instrument of the future: GNSS, opportunity to switch to geometric altitude and true bearing
There are two projects to replace the old legal references by modern ones more suitable for computers, and more accurate:
Confusion during the transition
There will be a transition period for the documentation to be updated. Today directions are magnetic and altitudes are barometric. There is no need to mention it on charts, as this is a requirement from ICAO (Annex 4 and Doc 8168). But at some point in time the assumptions will change. Without adding explicitly which references are used, it'll be impossible to decide whether a chart has been designed using the old or the new conventions. There will be a transition period where the conventions used have to be explicitly indicated.
Turkey authorities are likely adding the explicit annotation, in order to anticipate the need to know in the coming years: These charts have been designed with "magnetic bearings" and "altitudes MSL" (barometric).
"Tracks and bearings" vs. "bearings" only
There is a difference between a track and a bearing: A bearing is measured relatively to a fix or a facility, while a track is the direction of the path in general.
- On the holding pattern depiction in your question, 206° is a bearing. This bearing also defines the track of the inbound leg.
- On the other hand 26° is not a bearing, but a track.
It's more appropriate to talk about bearings (which also include radials) and tracks. Turkey likely updated their template in order to be more accurate, though this makes little difference here.
Altitude unit: Foot
Foot is a secondary unit for altitude. ICAO, deeply rooted in the Old World, has embraced its metric system since its creation, and stated since a long time the meter is the primary unit to be used for altitudes and distances.
Nobody used it when it was decided, a transition period principle was agreed, without specifying a deadline (typical of projects which are not going to complete). We are still in the transition period, and there is little craze for moving on.
So far a few States use this unit. The Russian Federation (as a legacy of USSR) and China do work with it as their standard. Russia, China and Turkey are all partly or totally Asian countries, close to each other.
It's possible the non-standard altitude unit (foot) is mentioned because of this proximity with large fully compliant countries .