kono apuri nara, sumaho de mo roguin dekimasu.

Here, なら means something like if it’s this app or when it comes to this app.

It often adds a nuance of:

• choosing one option out of several
• contrasting it with other possibilities
• saying in that case

So このアプリなら can feel like:

• If you use this app, ...
• As for this app, ...
• This app, at least, ...

It often sounds like the speaker is responding to some context, such as:

• Can I log in on my phone?
• Some apps don’t work on smartphones.

Then the speaker says: このアプリなら、スマホでもログインできます。

So the nuance is not just this app, but this app works / this app is okay.

The comma shows a natural pause after the topic/condition part:

このアプリなら、
スマホでもログインできます。

Japanese often puts a comma after expressions like なら, especially when the first part sets up the condition or topic for what comes next.

It is not absolutely required every time, but it is very natural here.

スマホでも is:

• スマホ = smartphone
• で = by/with/on, marking the means or device used
• も = also/even

So スマホでも means:

• with a smartphone too
• on a smartphone too
• even on a smartphone

The exact English wording depends on context.

If the idea is:

• You can log in on a computer, and on a smartphone too, then も feels like also.

If the idea is:

• Surprisingly, you can even do it on a smartphone, then も feels like even.

で marks the tool, means, or place used for an action.

In this sentence, the smartphone is the device used to log in, so で is natural.

Examples:

• パソコンでログインする = log in on a computer
• スマホで見る = watch/view on a smartphone
• アプリで払う = pay with an app

So スマホで means using a smartphone or on a smartphone.

No. Here, でも is not the conjunction but/however.

In this sentence, でも is made of:

• で
  • も

So:

• スマホで = on/with a smartphone
• スマホでも = on/with a smartphone too / even on a smartphone

This is a very common pattern:

• 日本でも = in Japan too
• 一人でも = even one person / even alone
• 車でも = by car too / even by car

ログインできます means can log in.

ログイン is a verbal noun borrowed from English login/log in.
It behaves like words such as:

• 勉強
• 運転
• 連絡

These can combine with する, and their potential form is often expressed with できる:

• 勉強する → 勉強できる
• 運転する → 運転できる
• ログインする → ログインできる

Then the polite form is:

• ログインできます

So this is the polite way to say can log in.

Japanese often leaves out the subject when it is clear from context.

So this sentence does not explicitly say:

• you can log in
• we can log in
• one can log in

The listener figures that out from the situation.

In English, you usually need a subject.
In Japanese, omitting it is normal and natural.

So ログインできます simply means can log in, with the subject understood from context.

It can be either, depending on context.

Most basically, も means also/too:

• You can log in on a PC, and on a smartphone too.

But sometimes it has an even nuance:

• You can even log in on a smartphone.

So スマホでもログインできます could suggest:

• smartphone access is included as well, or
• smartphone access may be surprising or worth pointing out

Both are possible. Context decides which one sounds best in English.

These are different.

このアプリなら

• if it’s this app
• as for this app
• has a contrastive or selective nuance

このアプリで

• with this app
• focuses on the means/tool

このアプリでは

• in/with this app
• can mark the setting or context
• can also sound contrastive depending on context

So:

• このアプリなら、スマホでもログインできます。
  = If it’s this app / With this app, you can log in on a smartphone too.

This sounds like the speaker is picking out this app from other options.

If you said:

• このアプリでスマホでもログインできます

that would sound less natural and more confusing, because now both このアプリで and スマホで could seem to compete as the means.

Yes. That is grammatical and natural.

But there is a difference:

• スマホでログインできます
  = You can log in on a smartphone.

• スマホでもログインできます
  = You can also/even log in on a smartphone.

So も adds the idea of:

• too
• also
• even

Without も, the sentence is more neutral.

They are loanwords, mostly from English:

• アプリ = app
• スマホ = smartphone
• ログイン = login / log in

Katakana is commonly used for:

• foreign loanwords
• some technical terms
• brand-like or modern-sounding words
• emphasis in some cases

Also, note that スマホ is an abbreviation of スマートフォン.

Usually, in a sentence like this, it is about what the system or app allows.

So it does not mainly mean:

• you have the skill to log in

It more likely means:

• it is possible to log in
• the app supports login on smartphones
• the system lets you do that

That is a very common use of できる with technology and services.

Japanese often puts the context first and the main statement later.

So this sentence is structured like:

1. このアプリなら = as for this app / if it’s this app
2. スマホでも = even on a smartphone / on a smartphone too
3. ログインできます = can log in

This is very natural in Japanese:

• set up the topic or condition
• add the relevant details
• finish with the main verb

English often gives the main idea earlier, but Japanese commonly builds up to it.